More information please...? What top end is on the car? What goals do you have? For $2500, you could easily have a 347, but that will do you no good if you don't have the parts to support it.
+1 $1300 for his 306 shortblock with forged pistons and rods. you would still have enough left to pick up a set of GT40 heads and intake off of an Explorer. You will probably have enough left for gaskets and other ends & outs. Depending on your H/C/I setup now, could be a step up.
I just put an explorer engine in my 95 for about $1400 that included a cat back flowmasters exhaust and some transmission work. If you were to go bigger cam and port the intake you could easily squeeze it under that budget. I had some parts that you wouldn't have had to buy like a torque converter, shift kit, exhaust, strut tower support, and intake adapter which totaled about 600 so you would have some room to play.
Check out my post about it on here or go to my blog. I have a list of all the parts I bought there. Http://www.nerddawg.com
Since it's more about getting the car going again and $ than performance, get on craigslist and find someone selling a used running shortblock or long block for 100-300 dollars and swap your stuff over.
If you want to build it, then give us a better idea of your goals, and if you already have anything.