Convertible sports cars tend to be expensive to buy and run. Used ones may be cheaper, but get the wrong one, and the servicing and repair bills will soon have you wishing you took the bus. However, if you know what to look for, there are some great used sporty roadsters out there that deliver an engaging driving experience without the fear of crippling running costs.Affordability is a nebulous term, but for the purposes of this article, we stuck to values below $20,000. Most enthusiasts will point to a Mazda Miata and say 'job done,' but we were after something a bit less predictable, and with a few more cylinders under the hood. The Porsche Boxster comes to mind, but good ones aren't cheap, and servicing costs remain at Porsche levels regardless of their age. After much deliberation, we realized that there was one convertible sports car that fitted the bill perfectly, and even though it drives like an old-school muscle car, it is modern enough to be used as a daily driver.For this article, we stuck to roadsters with prices below $20,000 that had a good reliability track record and reasonable servicing costs. All vehicle and pricing data was compiled from reliable sources. The Nissan 370Z Convertible NissanNissan has made a habit of keeping some of its models on the market for far longer than most rival automakers. The Nissan GT-R had a 15-year model run, and the 370Z wasn't far behind, as it was on sale from 2009 to 2020. It was already a decidedly 'old-school' package even at launch, following the recipe of its 350Z forebear. This meant a big V6 up front, a manual transmission as standard (a 7-speed auto was optional), and drive being sent to the rear wheels through a limited-slip differential.NissanEven in 2009, the market for naturally aspirated rear-wheel-drive sports cars was in short supply, and the 370Z filled that gap perfectly. It wasn't the quickest or the best handling car in its class, but judged as an overall package, it hit the sweet spot many customers were looking for. The roadster was a bit heavier and ever so slightly slower, but the ability to drop the roof and enjoy the sound of that V6 on a sunny day made it even more special as a daily driver. Plenty to Pick From NissanThanks to a long production run, you won't have any trouble finding a decent example for sale, although production figures tapered off dramatically from 2017 on. In total, 77,428 370Z's of all types were sold in the US alone. Updates were few and far between, with most annual changes being minor trim and kit changes. The venerable 3.7-liter VQ37VHR V6 engine was used throughout, with NISMO models getting a small power bump from 332 to 350 hp.The majority of roadsters were specified in Touring trim, which focused on comfort and luxury features, and even though the manual is a pleasure to use — and comes with rev matching — most customers specced their roadsters with the 7-speed auto. In practice, it suited the more laid-back nature of a convertible, and for those stepping into their first sports car, it may be less intimidating, too. What Is a 370Z Roadster Worth? NissanDespite the niche nature of a two-seater roadster, the 370Z Roadster has decent residuals, with 100,000+ mile examples still trading for over $10,000. Cleaner low-mileage cars are still selling for over $30,000, and it is between these two extremes that you will find the best deals. Always check for a full service history, as neglected maintenance can come back to bite you. What Else Is Out There? ChevroletThere were plenty of roadster alternatives to choose from during the 370Z's production run, although many were either turbocharged, all-wheel-drive, or couldn't be had with a manual transmission. The Porsche Boxster was certainly a contender, with a flat-six engine, rear-wheel-drive, and standard manual transmission, but you may have to look for a much older model year, and parts and maintenance costs can be high.FordThe Audi TT was never sold as a six-cylinder, and the Mazda Miata was an altogether more focused sports car that also never got anything more potent than a 2.0-liter four-cylinder under its hood. The most logical alternatives to the 370Z, then, were the sixth-gen Ford Mustang and Chevrolet Camaro in drop-top forms. Both were offered with V6 power, and had the added practicality of (tiny) rear seats.Power and performance figures were similar across the board, and plenty of both models were made, so it's only a matter of time before you find one to suit your particular needs. Looking at J.D. Power consumer data over a number of years, the Nissan 370Z scores highly in reliability and driver satisfaction, as does the Camaro, while the Mustang was rated marginally lower in driving experience, but had a great resale value. The NHTSA also shows the 370Z to have fewer recalls and customer complaints over its production run. In truth, there's not much in it, but if you want something a little more exotic and prefer two seats to four, then the 370Z is a great bet. An Off-Beat Alternative BMWIf you crave something a bit different, then another left-field alternative is the BMW Z4. The second-generation E89 models were initially criticized for being a bit too grown-up and more grand tourer than sports car, but this makes this generation a closer alternative to the 370Z. It also came with a metal folding roof, which offers a coupe-like experience. You'll want the 35i model, which was fitted with a turbocharged 3.0-liter inline-six and could be had in manual and automatic forms. Just be aware that servicing and maintenance can get expensive. Convertible Motoring On A Tight BudgetNissanMost people tend to think of new sports cars as expensive toys, and many start off that way. Older, neglected sports cars can also empty your wallet as you shell out for expensive parts and servicing. The Nissan 370Z is one of the few that offers the charms of a sports car – especially in convertible form – and doesn't cost tons to buy and run.It isn't the only option either, as homegrown offerings like the Ford Mustang and Chevy Camaro convertible are similarly affordable. The question is, which one will you be getting as summer finally starts to spread to most corners of the US?Sources: AutoTempest, BMW, Chevrolet, Ford, JDPower, Nissan, NHTSA