I want to ask for a quote, but I don't want the service provider to be legally bound to the estimate. What should I disclaim in my quote request?
The simplest thing to do is to just write "Non-Binding" on the quote itself or to stipulate same in the request for quote.
Either that, or you can write a complete sentence like what @jqning wrote:
"This quote is for informational purposes only and creates no obligations on the part of any party."
However, as @gracey209 commented, quotes alone usually do not create any binding obligations. Unless it's agreed by all parties in advance that it will. As in a formal bidding process. For example, if there were a closed bidding process for contract work, it might make sense for the bidders to be bound to their bid as a condition for having their bid considered.
However, that scenario does not seem match the circumstances you describe. If it did, then just leave out any binding language in the bid agreement.