How much gold does it cost to rebuild very small town?

I'm talking 3 dozen buildings max, and a cleric infirmary (a highly prestige one).

Considering the town will be destroyed by the end of next session, my party will want to rebuild from the ground up, and need to know what sort of costs I'm looking at so I can provide the necessary amount.

Town is inside of a canyon, space is limited. Lake in canyon has healing potential, that people people will travel across the lands for aid, from aches to debilitating illness, but they send more export rather than take in customers simply because they haven't the room.

But I don't know where to set costs, and types of buildings necessary.

Thanks!

EDIT: Getting fantastic answers, but it's leading to other thoughts. If say the entire town was working towards this project, how long would it take? I assume the next city they head to they can always send down hirelings as well.