I looked up an alpha design that uses two tubes
and found a Peter Dahl transformer for the thing
was $425. Ouch!

The Peter Dahl prices are fair but not exactly cheap.

Your best bet is finding a junker linear and "inheriting" the
transformer/bandswitching/inductor/capacitor and maybe even the plate
choke (although most junkers probably have a burnt up choke and maybe
some burnt up bandswitching).

I've pretty much decided on a single 4CX800A.

I assume you mean an ex-soviet "GU74B"? You can find a lot of designs
around the net using that part number.

Tim.