Like any airplane, it depends so much on how well it was maintained before you get it. You either buy a cheap airplane and put money into it in order to get up to your standards, or you pay the money up front for the best airframe and engine you can find and stay on top of it.
My Waco is a recent and complete rebuild/restoration. Original 1933 steel tube fuselage, struts, landing gear, but all the wood is brand new and it was a very thorough restoration. Virtually a brand new airplane and as such very little to fix yet. First annual revealed few surprises. Mags needed timing, tighten some oil leaks, top off the fluids. That's been about it.
Right now, my maintenance budget consists of annual inspection and oil changes every 25 hours (4 gallons of oil) and 12 gph fuel burn.
A Stearman shouldn't cost much more to operate IF you pay the money up front for a recent restoration. Otherwise, be prepared for anything. The one you linked is LOOKS nice, but is on low end of the Stearman price spectrum. A good Stearman will probably run you well above 100k.
Here is a good Stearman (priced accordingly):
http://www.platinumfighters.com/#!stearmane75/cwqn
I have flown that actual airplane (did my flight review in it back in April). It isn't quite as nice as my Waco, but a nice Stearman and shouldn't be a maintenance burden.