@bradf
It turns out that the stock tubes--even the 805--were not that expensive. I bought a replacement pair of 805s for about $90 each. I know some owners have replaced the 805 with much more expensive tubes, but I find that the stock tubes sound great!
The other tube types--300B, 6SN7, and 6LS7--are plentiful and vary greatly in cost, depending on what you are willing to spend to try different flavors. The stock tubes are really not that expensive. You have lots of choices for other types of tubes in these circuits. Only the 805 has limited options, in my opinion.
In short, this is the best tube amp I have ever owned. I am considering selling it only because I am currently trying a Lyngdorf 3400 and I am benefiting from the room correction and convenience. I just wish it had that wonderful SET magic that the LM 508ia has in spades.