were you thinking of building a full engine from the ground up with an ordered block and all the other parts or were you going to get a used engine and build it up I looked at the site and i think it would cost about 400 to 500 dollars to build up a full engine but you could probably skip some parts and use the originals if you rebuild an old engine some of the parts you could reuse without really having any performance lost are the whole block just replace all the bearings and stuff but dont reuse the old head and you should also reuse or rebuild the old ignition system unless you replace it with a better one which is usually expensive so really all you would need to buy for this method is all new gaskets and bearing all new piston,rods,crank,camshaft,head,flywheel and carberateur {i think got it all} as for the cost of a rebuild it would be somewhere around 350 or so i think
hope this helps