I don't recognized the OP's handle here, but I believe I know who he is, and that's he's been to my home and been given a ride in my ERA (: Funny enough, my ERA is nearly identical to what he wants to end up with. I'd sell him mine, be he seems to be a hands-on kind of guy who wants to build his own. I can't fault that at all.
If I was building on a budget, here are some considerations I can think of:
1. vinyl vs leather seats
2. No carpet or door panels (this is an FIA afterall)
3. Forget the heater
4. Forget the
oil cooler (coincidentally, I just bypassed mine recently and it's the best thing I did. Even with the additional
oil cooler thermostat it still allowed enough volume by to not ever effectively heat up the
oil to engine temp, even on a HOT summer day.)
5. Rear end has already been mentioned
6. STD street brakes work well. If you are tracking the car, you can put together better pads and rotors. You can fab some cooling ducts, too. You may not need the larger competition rotors.
7. Track the car without paint. You could drive the car a couple seasons and paint it later. You may enjoy tracking it much more without a nice paint job to worry about.
8. Wings and visors are nice on the street, but you could add these later, too.
9. Maybe consider using gauges other than the SW? They don't necessarily work all that awesome anyway.
You didn't mention if you were going for a period correct look or not, so there may be things you can't consider leaving out.
