Been over a decade since I messed with rebuilding engines - you have many choices. Used engines around here can be had for under $1000. Older ones are harder to find of course and updating has benefits but also pitfalls of getting everything to bolt up.

There used to be engine rebuilders in most towns, associated with bigger parts stores. Getting your motor rebuilt to stock by them (or use your choice of cam, etc) wasn't expensive and came with a guarantee. they'd hot tank and check for cracks, paint the engine, etc. I found them to be better than (cheaper) crate motors and not as much money.

If you want speed then a crate is often the cheapest way to go, certainly the easiest.

You can rebuild what you have if you want. If you don't have mechanical issues it's not expensive to get a bearing/ring/gasket kit, hone the cylinders. You can do the heads (have them checked!). If you suspect issues then it may be worth having the block checked and decked. If you stay pretty stock (crank, rods, etc) it's gonna be pretty inexpensive and very very satisfying to know you rebuilt your engine. Old motors are easy compared to today's alum/plastic/bolt stretching overhead cam motors.