How much $$$ Would having a layout designed and partially built be worth?

You would do fine! One trick I used is getting old sectional track (brass will do) and layout any thing you are unsure of, not that you will use it on the end product. Another idea is making templates of the track you are going to use, I used the old track method more though as I could push a longer than I intended to use boxcar to confim clearances of some tricky spots and since it was throw away track, I could slice and dice without worry.

I have another data point via the latest email from MR. There is a firm that will design your plan for $1,000 for up to 800 sq thread.

In another thread someone was asking about a full size track plan, that would be $3/ sq ft on paper 2-3 feet wide by 24 feet long.

The name of the firm is in the latest email.

Doesn’t look like the OP (original poster) has joined back in his discussion??