As said previously, with the cars being older and more expensive than usual for parts/labor, it can add up. I'm not trying to deter you from getting the SVX either, it's great.. but if you (your parents) don't have pockets to fix unexpected issues, you'll be walking.
I got my 94 with 163k miles and over the course of the past 40k miles (3 years, lot of sitting time) I've had to replace quite a bit but no transmission, thankfully.
First issue was a busted radiator around 168k. That was like $150 and I put it in myself. (shop was going to charge like $100 to do it.)
Then a coil pack went... that was almost another $100, I installed that myself as well. New spark plugs (reg maintenance) about $60ish... done myself.
You can't cheap out on tires either... well, you can I guess.. but even cheap tires will end up being like $400. (not like the cheap 13 or 14s most cars have) I had replaced those around 168k too and are ready for another set for sure (I'm at 201k now)
Other things I had to replace:
Battery - $130
A/C Pulley - $48
Idler Tensioner - $37ish?
Belts - $40
Alternator - $198
Power Steering Pump - $100ish
None of that includes labor as I did most of it myself (mechanics tend to hear AWD and SVX and equate that to BMW somehow...) I just roll my eyes and insist on trying to do it myself... except for the timing belt replacement.
Water Pump - $100
Timing Belt Labor - $300
Oh yea, one of the rims cracked so I lucked out and got a new set for $200 on craigslist.
But, if you're the OCD kind and super passionate about the car, nothing will stop you from keeping it on the road... except for money.
That and if you never plan to resale it, you're good. (Because you will NEVER get back what you paid/put in for it).