The low-level PCs
We are a party of an Oracle 5, a Rogue 5, a Sword Saint Samurai 5, and a Wizard 7. We have a contract on our heads, put there by an ex-party member in retaliation for some party members (without other party members' knowledge) putting a contract on the ex-party member. Yeah, it's complicated, and we can't get to her anyway, so it's not that important.
The high-level foe and his minions
The foe is a not-evil (maybe good) Cleric 15 and the cleric's force of around 25 pirate buddies. The cleric has taken on this contract more out of romantic desire for the ex-party member than for the cash.
In a town governed by money. Anything goes in this otherwise lawless town if the state's drawn up a contract permitting it. The town's laws, such as they are, support the cleric collecting on the contract.
The cleric and his force arrive tomorrow. Instead of dragging this out, we'd rather have this encounter now in the town and resolve this conflict, one way or the other (for instance, one way is we live, the other is we die). We have 1 day to prepare. Our funds aren't liquid, mostly tied up in our gear. It's likely the town has shady and dangerous resources available, like black powder and opium.
What can we do?
Is there a way for the party to win a fair fight against this foe and his force? Is there a way for the party to win an unfair fight? What other ways outside of the fight box are there to deal with this situation?
Note: The campaign's imploded since this situation, so answers relying on talking to the DM to point out the mathematical error in sending such a foe against the party aren't helpful nor are other metagame methods of dealing with this (for example, bribing the GM with money, pie, or special treatment for his character in the next campaign a current player runs). We never got the chance to deal with this foe, and I'm wondering how and if we could have dealt with him in-game.