You're right about a front sprocket being cheaper, but nothing wears out a chain faster than a small countershaft sprocket--and that is a handy way to regear using an existing chain. I'm buying a chain anyway, but thanks for your suggestion.
I've heard the wears out chain faster but chains are pretty cheap and how much faster are we talking I've owned a few TW's and have never seen a worn out chain from smaller front sprockets only from over all miles usually 1000 to 2000 miles on a stock chain and a DiD X-ring is usually good for 5000 miles
I guess I don't believe the chain knows the difference between 12, 13 or 14 tooth sprockets ( I speak in a whisper while changing sprockets so my chain doesnt hear lol) and if you ride so much you are wearing out chains a Scottoiler will solve any such issues
Just for info. I am about to order a new chain and a 50T rear sprocket from Rockymountain. It looks like they have a pretty good supply of sprockets. I did not look for a 55T like you are looking for but it might be worth a look. The 50T is $20 which seems reasonably priced.