How much would a contractor charge to paint some gable vents on a 3 story building. The vents are wood, half-rounds and range from 2' wide by 2' tall and as large as 6'x5'.

Your best bet is getting some estimates, wouldn't you think? <My guess would be, what part of the world you are from because this is actually the internet, and you don't say. Canada, US, UK whatever would all have different prices and procedures to do this work for you; so, call some painting contractors and get some bids going wherever you happen to be.

Tick

I agree with tickle, get 3 bids, they are free. You did not even tell us how many vents so its impossible for us to even try. Most of the painters I've worked with would not even give this a shot. 3 stories is a bit of a reach for a ladder and a scaffolding would cost you over $300 per vent plus materials and labor.