I saw a set of 17" steel wheels and hubcaps on craigslist for $60 and thought the backspace was too deep, but it got me thinking.
This will work, and there are new, inexpensive 17" steel rims out there, for trucks. As such, using them on your car will make it handle like a truck. At roughly a third more the weight of a steel rallye wheel, they aren't lightweights.
Mustang take offs and copies are the cheapest, lightest way to get into the 17" wheel game. Tires are another story, but if you stick with some smallish 245 and 255 sizes, it may not get too expensive.