I've read good things about Massey also, so they'd be my bet.
Costs can vary quite a bit. I've had BCS do one, but they aren't actually a CAT service facility with every ultra-current chassis service resource or CAT electronic gizmo on hand, and they cost more than CAT facilities since it took them longer and no discount applied at the time. I got a super deal at a CAT certified facility in West Valley City (Salt Lake), Utah, a couple years ago, where they full-serviced the engine/chassis and genset and the cooling system (new ELC) for less than $425, and $28 of that was state tax.
I'll likely never find a deal like that again. Commonly for just engine service it can range from $350 to over $500. CAT no longer makes motorhome specific engines and quit supporting them and sponsoring the CAT Club, which then switched its focus to all branded diesel engines. Along with that abandonment went any discounts specific to CAT products, so service now is 10%+ more expensive. It pays to call ahead to Massey and others so you know what to expect, but it's more important to have reputable work even if it costs more. Getting service while in a non sales-tax state, like Oregon, can save a little, and I personally prefer Peterson CAT, but that's inconsequential to you of course if you want service now.
Joel