I'm thinking 7.5" width is going to be the max in a 17. On a 7" rim though, I believe a 205 wouldn't be too much of a problem. Only thing is, I'd go with a 205/40 as opposed to 45 series. Mainly due to the speedo factor, as with 195/45R16s being standard, going to a 205/40R17 increases the overall rolling diameter by just under 7mm. Going to a 205/45R17 increases it by 17.2mm, which also puts you on the wrong side of the law in some jurisdictions (I know here in SA, you can fit whatever size wheel as long as the overall rolling diameter isn't increased by more than 15mm over stock). I used this calculator for those measurements:
http://www.exploroz.com/Vehicle/Tyres/SizeCalc.aspx
205/40R17s aren't that expensive from what I've seen. Kumho KU31s go for around the $90 bracket plus freight or KU39s around $110 each plus freight. Then I guess you need to factor in fitting, etc. and some tyre places will charge $20-25 per tyre for that alone. Guess it's a good thing I have a mate that can do it for free.