Any home brew tube amp will cost you:
Chassis + hardware + Power Transformer + Output Transformer + tube(s) support + tube(s)
You will find the price nominally breaks down like this:
($25 to $200) + ($10 to $40) + ($30 to $250) + ($20 to $250) + ($10) + ($2 to $50)
Now, you can do your own chassis for fairly cheep, 25 dollars or so, some sweating swearing and probably at least one metal cut thumb. Pre-purposed chassis can easily hit 100 and even 200 just for the piece of metal.
If you do knobs and lights and power cord and fuse and switches on the super duper eBay cheep you can keep this closer to the 10 end, going with "name brand" parts you will easily go to 40 if not more.
If you go with Antek and find a way around their 25 dollar shipping to Canada fee, they sell a $30 transformer suitable for a tube amp. Hammond is everyone's cats meow, and theirs is 250 dollars. There is a broad range between for pricing, but thats the high and low end of that.
OT's on the low 10W end start at about 20 dollars. You can do two 10W channels and use 2 10W OT's for less than 1 20W OT depending on who you go with. Hammond again is the cats meow and again is the highest priced part there.
No matter who you buy your tube sockets/resistors/caps from you will find that you will average 10 dollars per tube.
If you get your tubes from the exUSSR you will be on the low end of the spectrum as low as 2 dollars for the bottle, and honestly tubes can go into prices so high that it no longer becomes a fun hobby. However, I think I see tube prices maxing around the 50 dollars each mark at L&M, me personally, I buy exUSSR.