Miss Maylene

Build what your wallet can handle, LA engine would cost you less.
Probably. Depends what you do to it. A back yard shade tree rebuild would be cheap,but dont expect much more than 30 to 40 thousand miles out of it. Reusing all the stock stuff for either option might keep costs down. Going big block requires a big block bell housing trans,correct engine mounts,good rad and cooling system,probably a different driveshaft and definitely a stout diff. It's not just the big block ,but all the support systems that will withstand it's punishment that add up. Heck not even a stock 8 3/4 will hold up without at least upgrading the axles.
The stroker 318 would need some stout upgrades too no doubt. Torque wrecks stuff,lol. But you already have the 318. I'd at least open it up,have the bores inspected,see how thick they are. Rememer you sure can bore it out,but it has to be able to take it.Overboring thin walls can lead to overheating and loss of cylinder pressure,as the bore just isn't round under duress.So make sure you have a good block ,magaflux and sonic checks. If it's no good then this may infuence your decision.

Keep your eye open for deals. Something may fall from the skies..Lots of times shops have abandoned projects their looking to be rid of.