That's part of the problem, not having any luck finding anything in a 25 or 27 crt and I really don't want to drop 600 on a Mak.
I ran into a similar issue recently... it's mostly about being patient and keeping close tabs on Craigslist or other local listings.
I bought 3 San Fran Rush sit-down cabs. 1 had a good monitor, 1 had a monitor that worked but a really crappy picture and the third was missing a monitor because the previous owner had cracked the tube and threw it out. I wanted to keep 2 of the machines and fix up/resell the third so kept an eye on craigslist. Further, the machines I was keeping I wanted to use tri-syncs since I wanted the option to run MAME setups at 640x480 instead of dealing with medium resolution.
after a few weeks I found someone selling a pretty much brand new a 27" Makvision for $100... some kid who thought he was going to build a machine and never got anywhere... obviously this was an amazing deal but ... a couple of months later I found someone selling a "Faster than Speed" sit-down cab for $350. i didn't have room for the machine so I offered to give him his $350 asking price if he let me strip and take just the electronics including the monitor, he agreed... I resold the Atomiswave setup and a few other parts and got about $300 back out of the deal leaving me with a beautiful $50 Wells Gardner D9200... and some other lucky guy got a sit-down driving cab with a wheel, pedals, and a seat for free since the seller gave away what I left.
It took a couple of months of diligently and patiently watching Craigslist for the right deals but now I've got 2 great tri-syncs to go in to the two cabs I'm keeping and 1 good medium res left over to go into the cab I plan on reselling.