Actualy 351's are tons cheaper!!!!!! You will make tons of power per $$ spent... But if you are really looking for a cheap build do a 460 bbf They are easy to find and parts are everywhere!
Everything is just bolt in and you dont need computers or anything
there are other issues around doing a 351w swap that, frankly, you are not ready for just yet.
that said, if you have a friend who knows what he is doing, you could probably get one and get it in for $3000. but it would probably be more than a weekend project