Define cheap?
I buy those poster frames from Michaels at 50% off then cut them down to fit the translite (use a long straight edge). I also use the super thin 3m double sided tape to keep the edging in place. Not sure what it is called but it is little more than a really sticky adhesive. This is about as cheap as it gets. Down side is you can't get the translite out easily so not so good as storage.
There is a guy on here selling light boxes for Stern translites for $125 shipped and all you do is swap the whole glass in and out.

http://www.spotlightdisplays.com/pinball-translite-frames.html

spotlight displays! Frame is perfect, all edges open from the front so can be swapped out while hung or mounted on the wall. Ships with clear front and back covers for protection.

I bought one and it really impressed me, couldn't have asked for something better.

Pretty sure there is a pinside discount too!..but I don't remember it... PINSIDE in caps maybe...

I was going to recommend the one below, but it's $56 now! It was $23 when I bought it a couple weeks ago.

http://www.amazon.com/gp/product/B004EJMS4Y/ref=oh_details_o01_s01_i00

Also, I used this for a WOZ translite, so you'd want to measure a Stern to make sure it would fit.

I pick up cheap oversized frames at Walmart for ~$11 a pop

I went the Michael's route too. Got them for like $18 each after the discount.

I checked Wal-Mart too, but at mine, they were about the same price as Michael's (after the 40-50% off). I liked the ones at Michael's better as the hardware on the back was a round slider versus a metal tab.