hf1

You are likely to have a negative experience with any 987 that you get on that tight of a budget. I'd be looking for a clean, low mile 986 with LN IMS bearings done ($2.5-3k job). Also, best to find/have a good indy Porsche mechanic that you trust for any 10+ year old p-car. Well maintained 986/987 Boxsters will give you the best roadster bang for you buck including maintenance but your expectations must be realistic. If a $18k budget is "pushing it" and you can't easily swallow a random $4-5k service hit on a 10+ year old Porsche, then your happy/sad outcome will be like playing the roulette.

choeglund

2006+ 987.1S (with 3.4 engine) have an internal IMS bearing, only serviceable by splitting the engine case, which no one does on a preventive basis. Fortunately the failure rate on the internal bearings is very low. If you buy a 2005 or earlier Boxster S (with 3.2 engine), then IMS is more of a concern. At your price point and desired mileage, I think you would be looking at 2005 or earlier model, so look for a car where IMS has been done or plan for it in your budget. Once past the IMS issue, maintenance costs are highly dependent upon how much you can do yourself. Parts costs on Porsche's are a little high, but labor is where wallets get busted.