"caps for the at853rx mics can be had for $28/piece, but the omnis are discontinued, fwiw. you said your 933s may take those caps, but who knows, post to team At a boys for the answer to that one."
The place with the $28 caps did have white omnis in stock for a while. They may all be gone now. Also, keep in mind that the new line of AT mics that are replacing the unipoint series (AT853, etc.) have caps that will work with the older series mics (AT853, etc.) Don't know if those caps are on the market yet, or how much they will cost. Doubtful that they will be found for $28, since they are 'new' on the market.