A guy on a budget has to work with parts that are readily available. So you find parts that you can actually buy and type them into PipeMax and see what you get.

If the budget is big enough to handle custom pistons then that is one thing that can be played with. Same with ported heads, custom valves, etc.

Custom strokes and custom length rods are usually off the table for a budget build. A racing block with larger bore size may be in or out of the budget.

An "off the shelf" engine can usually be within 10% of a high budget engine if you use something like PipeMax to make good design decisions.