Have you considered making a cage? Hardware cloth works well. I've used it with my rats, and it should have versions that are narrow enough for mice.
Here's some links to building hardware cloth rat cages (which you can adapt for your mice's needs) to get you started:
http://www.ratbehavior.org/CageDirections.htm
http://www.casualhacker.net/blog/build-your-own-rat-cage/
https://bunnyrabbit.com/price/cagequip2.htm
Also, look into Martin's cages. They have 1/2 x 1/2 inch wire mesh. They're cheap for what you get. Make sure you request 'powder coating' instead of galvanized as plain galvanized absorbs pee odors and deteriorates much faster:
http://www.martinscages.com/products/cages/hamster/
Here's some links to building hardware cloth rat cages (which you can adapt for your mice's needs) to get you started:
http://www.ratbehavior.org/CageDirections.htm
http://www.casualhacker.net/blog/build-your-own-rat-cage/
https://bunnyrabbit.com/price/cagequip2.htm
Also, look into Martin's cages. They have 1/2 x 1/2 inch wire mesh. They're cheap for what you get. Make sure you request 'powder coating' instead of galvanized as plain galvanized absorbs pee odors and deteriorates much faster:
http://www.martinscages.com/products/cages/hamster/