When a hero buys services, use these rules to arrive at an asking price and a bare minimum price. In most cases, the arrived-at cost is per task performed on the hero's behalf, regardless of how many skill checks are involved.
These rules are specifically for buying services, as opposed to labor that results in tangible merchandise.

Determining Cost

Every service has an asking price and a bare minimum price. The person providing the service starts by asking the highest price he thinks his services are worth, expressed as a Purchase DC. This number is equal to his total skill modifier for the appropriate skill, multiplied by 1.5, rounded down. If two or more skills apply, multiply the average of the skill modifiers by 1.5 to arrive at the Purchase DC. If no particular skill seems to apply, use the character's Profession skill modifier. If the Purchase DC is fewer than 2, the character refuses to take the job-or takes it, then badly bungles it.
A hero can attempt to negotiate a lower price with an opposed Diplomacy check. For each point by which the hero beats the supporting character's Diplomacy check, the Purchase DC drops by 1. But for each point by which the supporting character's Diplomacy check beats the hero's, the Purchase DC goes up by 1. You can take 10 or take 20 on this check (as can your opponent). No retries are allowed. Haggling the price in this fashion can never reduce the Purchase DC to fewer than the supporting character's skill ranks in the relevant skill (or average ranks in the relevant skills), multiplied by 1.5, rounded down. This is the bare minimum price; doing the job for less starts costing the character money.