Can't speak specifically about the 555, but I bought a Ford 755 TLB about 6 yrs ago. Tires were in worse shape than the one you're looking at. Replaced the fronts over the last couple of years, few hundred bucks each, mounted, IIRC. Easy enough to call a tire place and get a price. Have had tubes put in the rears due to flats and there's not much tread but..... this machine cost me under $10k. I put my own driveway in with it which paid for the TLB by itself. I've used it to transplant trees and have dug countless stumps, reworked my property, dug ditches, etc. Yes, it's a tired old machine (1980) and the pins are a little sloppy, but I'm not making my living with it. One of the bad things about heavy-duty construction equipment is the price of repair parts. But I've been able to find the things I've needed online and avoid the pain of the NH/Ford dealer pricing. I've replaced a fair number of the hydraulic hoses due to leaks and I can even get a complete engine rebuild kit for around $500 if I need/want to do it. The scariest ($$$) thing would a failure of the shuttle transmission, but a Ford mechanic told me they're pretty bullet-proof. Not sure if it's the same design as on the 555.
I also own a Ford 3600 tractor which is a great machine. Cost me under $5k. Yeah, Case is a real popular b/h and Cat makes great equipment but for what I use it for and what I've got invested in it, the Ford TLB does me just fine.