Hello Emma,
I've made large display cases for a restaurant [1:48 Bounty and 1:96 Cutty Sark]] and for that I used the plastic sheeting sold at that famous DIY shop (and is a short form for eating outside and cooking on charcoal B BQ).
The case(s) have been in place for over 12 years without damage by person, though I am to check them this year for any sun (UV) damage. One sits on a large window ledge, the other, the Cutty Sark, is high up on a wall and diners can sit beneath it and look up through the bottom as thats clear too. I did mine before the fire!!!!
I looked into the costs of display cases made by the professionals, and they can be very expensive, but it does take time to make a decent job, but the cost you quote for acrylic seems high.
I'm in the Isle of Man so no help to you, sorry.
Hope this helps, Kimosubby