I have a 1990 bmw 525i, the front defogger doesn't work, I'm pretty handy but I don't know anything about cars really. Is this fixable on my own or should I just take it to a shop (price?) The only self solution I've thought of is installing a mini heater on the dash haha.

Does it not switch to defroster mode or is it not blowing any air or is it not blowing any warm air?
How long has it been like this and what has been done so far to fix it.

It blows no air, the air conditioning doesn't work either. It's probably been like that for a few years, I was just given the car and as far as I know its been neglected.

No air means the fan motor isn't working. That may be either the speed control or the fan motor itself.
Now the 'A/C doesn't work' needs a different diagnosis altogether.
Can you fault trace these or do you plan to take it somewhere?
Experience and the correct tools can make this quick and relatively painless.