Be zen with your ram....
I believe you really Really need to have some internal dialogue with yourself and decide what you really have the funds for and what your expectations are.
After that the answer wil present itself. And you can proceed with a plan that will meet your expectations, maybe exceed some.
But lets be honest, if your a 21 year old kid with a small tool gbox and not much of a indoor work area, a 4BT swap is gonna be tough. BTW I've seen it done under crude conditions, but it isn't all that impressive.
With the 318, you can build a nice reliable toy that should niether break your budget, but probably won't break any records, except longevity. Otherwise the sky's the limit.