Welcome! With that kind of budget to buy a NA (first gen) I'd be in heaven! For a little comparative info, I bought my 92 in 01 for $4500 and my 90 about 3 yrs ago for $3700. Don't remember the miles on the 92 when I bought it, but my 90 was in mint condition, always garaged, EVERY receipt (including oil filter labels! OCD Jewish architect I got it from!), and 122k miles.
Good luck finding a nice one. Great shifter & factory clutch to someone how to drive a manual. I was somehow able to teach my sister and several cheerleader friends how do drive a stick in my Miata!
*Oh yeah, to anyone who has seen my car and going how the hell was it in "mint" condition when he got it! I've added 117k miles, had a fender bender, and been to probably 30 track days and it's certianly starting to show!