Anyone know the starting prices or have an example quote from distributed DNS services that provide service for high queries with SLA agreements such as Neustar ultradns?

What is your definition of "high volume"?

With respect to SLA's, there is little that an SLA will do for you in terms of actual performance. The role of an SLA is to determine how big a pound of flesh you get to extract from the vendor in the event of a breach, and as a means of spreading the blame around.

There is no vendor who deliberately sets out to have unreliable services. Therefore, when someone starts off a conversation with "SLA", it rings alarm bells.

The question then becomes, "why" someone would care about an SLA above all else.