We have a place local that sells LEXAN, it's called General rubber. I Would check the yellow pages of the closest city and see if you can't find something like them. I think a sheet of lexan was about 250 the last time I checked. I run the grade right below LEXAN, it's polycarbonate It's pretty much the same as lexan only lexan is a brand name. I think it's about 100 bux a sheet. You can get one car out of a sheet if you lay it out right. Don't let them sell you the plexiglass thats cheeper. It scratch's way to easy. and is not as strong.
I clean mine with windex and T-P, if it's soft enough for your ass it will be OK on the plastic. Try not to use paper towells to clean it cause it will really show over time in the fine hazeing of scratches.
I run 3/16 for a windshield
Most places that cater to pilots sell a "plexiglass cleaner"[in my military helicopter flying days we called it bubble polish]to clean and apply a scratch inhibitor to the surface. That works good as a cleaner and such. Might try looking for that.
AS far as something to clean the glass with we were told for plastic windshields on bikes to NEVER clean the windshield with anything that had an X in the name. Got some stuff B210 from the bike shop and my 5 yr old glass looks like new.