Good work on making the effort to save it.
I've had a similar journey on our project car now. I'm into in a little beyond the budget you noted but a chunk of the things I'm doing are completely necessary and are just, since I'm building something for myself that I intend to keep, I may as well do...
In our case, it's gone from a biege interior to full charcoal interior, dash swap, rooflining retrimmed in charcoal, etc. I bought a parts car for all the small parts I thought I might need and the larger parts ended up coming from about 5 different cars now. If you need some sort of small grey trim oddity, drop me a PM. I'll go through what I've got for you.
The parts car has been well picked over now and it isnt far off being taken away but its possible there'll be some weird bit that you might need.
Looking forward to your progress regardless.