Made a very cheap city battle mat for warhammer 40k using painters drop sheets, sealant and paint. Here’s how you can to!
Dust sheets (enough for a 6×4 battlefield will cost you around £3) https://www.ebay.co.uk/itm/Cotton-Twill-Dust-Sheets-Various-Sizes-DIY-Builder-Decorating-Cover-10-8/114118900926?hash=item1a92043cbe:g:iSAAAOSwCgleSk5X&var=414378904137
Acrylic bathroom sealant / caulk: Buy at least 4 for a 6×4. Its not cheap online(~£7 per tube) so go to a dollar store, pound shop, home bargains etc and you can find it for £1/tube.
Acrylic paint: Just buy the cheapest tubes you can find on ebay for about £3. There are lots!
Good luck!
Source
Looks great! Does the acrylic crack at all when rolled or folded?