We have a '94 in our family and it runs great, it now has almost 100k miles. We have never had any major problems whatsoever and all the tech still works very nicely. Even the leather is in mint condition.
The maintenance costs include just the usual stuff, tire rotation, oil change, etc. Nothing 'interesting' to talk about. So it's not expensive
Besides the grille, I do not think there is much difference between the '94 and the earlier models. What I have heard is that the 1st gen. actually accelerates a little bit faster.
Looks like '91 is the newest model he will be able to get with $6k -
http://www.edmunds.com/used/1991/inf...q45/index.html
But, since the '91 IS 3 years older than the '94 that we have, I really can not say much about it. If things do begin to break down, it will be pretty costly I imagine.