OK... Is there an affordable way to do this?

Velcro ain't cheap. Precut stuff at Office Depot is like $4.99 for 32 square 5/8" chunks. One square foot needs 144 velcro squares. A 20" X 30" Foam Core board needs 600 squares. (Perhaps 1.5" chunky is better.)

If I buy a rolls of velcro I need about 20X2.5' or less than 50' of velcro. (15' is like $25.) 3 rolls costs $75.

I found 5/8" round precut black chunks. ($9.00 for 75 chunks.) Has anyone had experience with the round velcro? It seemed thicker.. so I wonder if it will be wobbly. (About the last thing I want is the front door to the dungeon tilted out 45 degrees...)

I'm hoping to use this with more projects. i.e. drop the floor squares of the Mars Command on the foam core base.

Try checking the dollar store. I think that I've seen precut circles or squares there. And I know that dollar tree has a varity of sewing supplies. But I'll have to check next time I'm up there to be sure.

This reminds me I need to see if felt will work the same way. I know I mentioned it a while ago but felt to felt should have enough adhesion that the pieces will stay in place.

And it's much cheaper than Velcro(r).

Yes felt will work the same way.
The stick isn't quite as strong as vecro, but it will hold up to someone knocking into it with no problems.

I actually use a felt puzzle mat as my base I put the velcro on.
It's black and has a couple sticky strips on the back that keep it from sliding on the table.

Velcor is not cheap at stores.

I get LARGE rolls of it on ebay. Normally green or black. Really cheap that way. I think I got 200 yards of Hook and 200 yards of Loop for $12.00 (£6.00)

It's not as cheap as ebay, but McMaster-Carr (www.mcmaster.com) has 50'x1/2" rolls of velcro for under $40.

Geoff