If you are considering parallel SET, be aware of the issue of one tube in a channel pair becoming much stronger than the other such that, in short order, you lose the full power capability of such amps. Even when one starts with supposedly matched pairs, they tend to quickly become unmatched. I've had this happen in my Audio Note Kageki, and others running parallel SETs have noted this issue too.
I have my doubts about any "cheap" 845 amp. Many really don't run the specified plate voltage for that tube, and the ones that do, would have to be properly built to be safe to operate, and that means higher cost. The same would apply to 211 and other higher powered SET tubes.
I hope the $2,000 budget for a 300B amp is the budget for something used, and is not the budget including the output tubes, because decent 300b tube would eat up a very significant part of that budget. That would leave not much for other parts, particularly the output transformer which is not cheap in a SET amplifier. If you can build your own gear, the 300b kit offered by Elekit sounds decent and is quite inexpensive for what one gets. But, I still have my doubts about "budget" SET vs. the many inexpensive vintage pushpull amps that are available. There is no inherent superiority of any particular design, and a good pushpull transformer amp and pushpull OTL amp can be the right choice to deliver the goods.