I've got over 146,000 on mine and it runs great. I take the stang on business trips which can be as long as 6 hours one way and I've never had a single problem yet.
I get most of my fluids flushed/replaced yearly, oil changed every 3K, and a tune-up every couple years. A few things have been replaced like the alternator, battery, starter, and waterpump, but those are easy replacements which are commonplace. Some may be more agressive with maintenance, but this has allowed me to take my stang anywhere without the fear of it breaking down.
Listen very closely to the stangs you're interested in. No radio or A/C during test drives, just pure motor. A T-5 should last a good bit on a stock motor unless the owner has driven it poorly and too agressive. My T-5 is still bone stock with no servicing except for the fluid change. IF you're not very familiar with driving a manual, get a buddy who is to feel the car out.
$4,000.00 sounds alright. 5K is a little much possibly.