Annual maintenance excluding tires on my coach is about $500. SpeedCo does my oil changes, lube, filters and SCA testing. I paid $289.00 for this service in March of this year. They will let you in the pit to watch them work and will also inspect for any "issues" they may see. I found a leaky seal several years ago. Brake pads will last a lifetime, other issues will be regular maintenance that needs to be done at various intervals. I budget the "extra" $200/yr to cover those expenses. Things to carry extra would be extra fuel filters and an extra drive belt.
You didn't ask but know how to drain your air tanks, where your fuel and oil filters are, how to bleed out any water in the fuel system and the correct process to restart after a fuel filter change. All easy processes but often overlooked. You don't want to learn these things while on the shoulder of a Interstate.....Dennis