Welllll, you have to know what is really going on for a complete understanding. Like the General's 305 and Ford's 302, the 318 was Mopar's bread and butter engine. Now this part I am hard pressed to understand, they all had cams that were created with 0.030" to 0.050" less intake lift as compared to their 350ish cousins. None had decent vaccum, power or fuel economy, in the name of clean air. That is where all got a reputation as crap engines. The Ford did not get the rep as bad, but when Ford cam out with the 302 HO, it had a 351 cam and firing order. All you had to do to wake them up was install the 350ish engine cam and voila. Now going one step further to and "RV" cam with 204/214 at 0.050 and 0.450" lift really got them on par.
Now your comment about money, a 340 is going to cost even more for a core engine. Pistons, rings, bearings and gaskets, all other things being equal will be about the same cost. During overhaul, installing bigger valves and some pocket porting or springing for after market heads will help the 318. If you need to grind the 318 crankshaft, a 392 stroker kit with pistons, rings and bearings is a minimal extra cost. Add the $1,000 for a core 340 to its get it on the road cost and my money says you saved nothing.