Over the last 35 years I have purchased literally a couple of hundred used fountain pens. Out of that I have only had about 4 that I can remember that had issues. If you get a good deal you can have a typical FP restored for under $60.00 or so, barring any catastrophic issues.
Don't be afraid. Do your research and you will come out fine.
My recommendation on a FP choice on the more reasonable side would be a Platinum 3776. You can pick them up online for about $70.00 t0 $90.00. The Bourgogne is really lovely and the nibs are superb.
EX:
https://www.ebay.com/itm/Platinum-37...UAAOSwGTNfG6g5