Well, your consumer rights vary from state to state. If this kind of thing happened in my shop I would present you with a tear down estimate. A tear down estimate is required by law in my state and it is defined as an estimate that will cover tearing it down AND putting it back together in the shape it was in BEFORE you took it apart. It is not a repair estimate but it is still going to be closer to the price of a full blown repair than the price to simply pull the head and look around. I would present you this with the condition that if we got in there and it was apparent that I had installed the belt incorrectly or was responsible in some other way then I would eat it and if it was due to some other factor (i.e. failure of another component like the tensioner or something) then it would be your baby. The real fly in the ointment here is that you have to be dealing with an honest and ethical shop. If not I garuantee they can and will spin it right into your court. In the event that the shop simply stone walls you from the get go your only options at that point are to walk away to another shop or to inform them that they can expect a visit from the BAR (bureau of automotive repair) or whatever the equivalent is in your area.