My 2 cents.
As E30s are more mechanical than most of the younger BMWs, its a good car to DIY on. If you can remove brakes pads etc, changing oil filter should be a yawn. Same for the plugs/batteries/fuse/lights - typical consumables lar. Some of us are a bit more adventurous and like to open instrument clusters, play with the SI IC board....
Parts wise - as already concluded most parts are available although some like ECUs, Meter Clusters or some trim could be harder. I suppose, if you are resourceful - buying abroad from other BMW forums i.e. UK will be possible. Of course, some parts like Dashboard are hard find especially local.
Aftermarket parts - especially branded ones are harder still, and I would lump Bodykits and Wheels as good examples. Wheels for E30 are unique and branded ones like BBS or Alpina are.....rare and sellers charge a premium. Bodykits.....are also pricey and if you break one, you have to buy the complete set and RM3000 are not uncommon. ( this reason my car is plain jane )
Do expect some of the bigger workshops to shy away from trouble shooting your car when problem strikes......for them, time is indeed money and their Service bays, income generating space,
All in all - no matter what engine you choose, a E30 ownership dun have to be expensive especially if you are a DIY guy but do find a good body to start off with. ( unless you are a DIY panel beater/spray painter too... )
The rest can be dealt with slowly.....with some money.
Have fun!