I'm looking to build a bike up from a frame. I want to do a Gates belt drive with a Rohloff. I'm having trouble finding a good frame for the project. I really like the Budnitz style but way too expensive for me. My guess is a frame only from them would also be too spendy even if they sold frames seperately.
What others are out there? Or should I buy a used and modify?
The closest I can find is a Surly with the interchangeable dropouts. You still need to cut the frame but the dropout bolted on joins the stays.

2011 Raleigh made a bike that used gates belt drive. see if you can find one of these frames used or a NOS bike from a dealer.

Tout Terrain has a different approach the dropout is split in Half,

1 on each tube so when clamping the hub in the dropout , it holds those 2 parts together

Tandem eccentric BB, tensions the belt.

German framebuilder .

Bike Friday uses a single arm swingarm like , dropout slides to tension chain/belt

Elevated above the drivetrain chain stays also let a belt be un broken to fit..