Actually if you look at the Jobo 2520 with 2509n reel, you can do up to 6 sheets at a time, with a time proven industry standard tool, which you can get used for under 140$ or new for 169$.
You can use the tank for inversion (though that is very un economical chemistry wise with 1250ml needed), or you can rotate it on any flat surface, with them minimum chemistry needed for 6 sheets being 270ml. That said, as you note, with BW you will need to calculate the correct min active material per sheet amount, which might be greater then 270ml.
I thought the minimum requirement for the orbital was 500ml, but 200ml is as good as any other solution.
Expert drums are more expensive, but for what they do - they are more then worth the extra cost.
I think the OP is looking for some readily available, and non expensive way to process 4X5 that will also yield proper results, (all options suggested in this thread are better then an FR tank, some more readily available then others), that said - the MOD54 and Jobo options have the most answers to the OP's initial questions.