I think we have built our bus three times before we were happy with it. Keep your eyes open for certain items your looking for. tempestsearch.com
is where we found lots of our goodies. You might have to drive a bit but the savings is worth it. We got our 5500$ fridge for $800( fan was bad and returned to amazon guy worked there and was selling them), our washer/dryer combo 2000$ we got for $400 new from overstock, flooring from closeout store 100$ for the entire bus. But he best is my Cummins generator 5500 efi for 500$ ( guy bought a service truck for the front end he crashed and had no idea what that gen set is worth). Be very careful buying electronics like transfer switch or inverters. These things are just best to buy with a warranty( dont tell them its in a school bus) first words have always been "we dont cover school bus installs this was made for a house".
Good luck with your build!! This site is full of people that will be glad to help you along every step of the process.
Really good folks on here that sure have helped us.