Best place to pick up 20 gallon high glass aquariums?

I'm going to be putting together eight planted vivariums, and have decided that converting 20 gallon highs into vertical front-door opening cages is going to be the best way to go.

Anyone know where the cheapest place for me to get aqueon/all glass aquariums from is? I wish that I'd decided to do this like a year ago when petco had their $1/gallon sale.

I'd go the craigslist route but I'm having issues finding the right sizes, and I also don't know if all 20 gallon highs would have standard size trim around the rim for conversion purposes.