How to calculate vacancy for a seasonal place?

[Ryan Detzel]

There is a good deal on a short sale in a localish large (300+ units) summer only rental spot. It's listed for $20k less than all the others for sale and the sellers agent said the bank previously accepted this so they would again (buy dropped out). We've been there a lot because friends of ours have a place there so we're thinking of buying this place, spending the extra $20k to really fix it up nice inside and try to rent it out. Since it's in a complex the condo fees take care of everything except Internet, so that's one less thing to worry about. We basically would just be in charge of renting and cleaning. I ran the numbers and to break even we have to rent it for $1800/week (normal is $1700-2100) for eight weeks a year (July/Aug) and anything after that would be cash flow. The place is open for six months out of the year but from our research (friends that live there) it only really rents during the hot months so we're thinking we might be able to charge 1/2 or less for the other months just to get some extra income. I'm having a hard time determining if that break even point is good or not, even if we miss one major week (Jul/Aug) I would hope we could make it up on the other months but I'm just not sure as the data is sparse because most people rent through the complexes rental pool so we can't find vacancy information. 

The complex offers a rental pool and they manage everything but they take 30% off the top, with those numbers it's hard to make it work since it would have to rent for ~10 weeks instead of eight just to break even and looking over their site it appears they have 25 units for rent right now. They charge $2100/week, we'd undercut that on rental sites at $1800.

Thoughts? Are we overlooking something? Thanks