Looking to swap out my 11-23 cassette for a 12-25…I’ve finally come to accept that I’m a fat bastard, and a 25 would be really useful to haul my ribs-steak-and-beer consuming arse up hill.
Any recommendations for the cheapest place to go online?
www.totalcycling.com, but buy in bulk.
Alternatively, www.cbike.com has been pretty good, and www.supergo.com had the chorus cassettes on sale a while back. You can always try eBay, too.
BTW, I ride a 13/26, works really well for me. I ride 11/23 on my compact cranks.
Try ordering from Ernie @ www.procyclingdiscount.com . He’s a cyclist and more importantly at this date he is from New Orleans. He was just allowed back to his home two days ago.
It certainly would be thoughtful of you at this time to help support their economy. You can email him @ ehmahlman@bellsouth.net .
He has great prices as well. 
Good Luck.
Try this site to compare prices of bike stuff… http://www.comparisonpricing.com