Prototyping large tiles

That's exactly what I did the first time around for my modular board tiles. I printed them on paper and spray glued them to foam board and cut them out. I'm in the middle of making a second copy of the board since I reprinted the tiles 15% smaller but this time I printed them on sticker paper. It's a bit heavier and it eliminates having to use messy spray glue. I'm assuming it will last longer too.

Are your 8x10 tiles rectangular? If so, printing them on the sticker paper and sticking them onto foam board won't require a lot of cutting so it shouldn't be too much work. I spent 3 hours last night cutting mine out though since my tiles are made up of 19 small hexes so they take a while to cut out with an exacto blade. If you go to my profile and click on my website you can see what mine look like. They have worked really well so far for playtesting. Just printing your tiles on paper might be a bit flimsy and move around on the table a lot. But you could always test it out.

That link shows craft foam which is not rigid in any way .. it's just a piece of floppy craft foam. Many dollar stores sell foam board which is rigid (basically a styrofoam sheet with paper on each side).

I would second the chipboard idea. You can also use picture matting to good effect and can sometimes get off-cut pieces from framing stores for dirt cheap.