What should I upgrade first on my budget system?

@coryb

Room treatments are pretty boring. They just hang on the wall and not much fun to play with. But, as other’s suggested, I’d make these the #1 priority in your upgrade plan to improve sound quality.

I’d hang a better cartridge on the end of the tonearm.

IF the Rotel has digital output(s), a good DAC will add rocket fuel to your physical media.

You mentioned you’re in Montana. Sorry, just couldn’t help myself and added this link.

Frank Zappa:  Moving to Montana

The right Cd/amp power cable upgrade can be as good as new component.

@digsmithd +1

I would not call it a budget system.

Biggest bang for the buck? The turntable?

I know nothing about your speakers but they look very serious. Not the best match to your amp though, depending on your space/room size  (very broad generalization: if you are in Montana, your room may be big :) )

Room treatment, power conditioner, OCC interconnects and speaker cable, isolation footers, etc.