I take it you mean icons of touristy buildings based on photos? More pictures than icons? That sounds like there's a pretty big design effort involved, which would be reflected in the price.
A short version of the process is:
- Try and determine how many hours you'd spend on it.
- Try and determine your hourly rate
- Add in a little margin for uncertainties
It isn't always that easy though. Especially that first step, trying to determine how long it's going to take you, requires a great deal of prior experience.
My uncertainty margin is 1.5 the time I think it will take. It's usually ok to compensate my tendency to underestimate the time it will take me and a couple of corrections asked by the client.
As for an hourly rate, you could start by what you think would be a good hourly rate if you where working for someone else (on payroll).
I read an article (I need to find it back), saying that you can take that rate and multiply it by no less that 1.8. And as you gain experience, that ratio is going to be higher.
So let say you had 20$/h , you need to charge at least 36$/h. with the extra 16$, you'll pay insurance, cover your sick days (that are going to be unpaid...), office furnitures, ... It also take into account that you won't always be working 40 hours a week...
At least, it make sense when I read it...
It's not exactly that one, but it could help: http://www.zerogravity.com.au/blog/2009/05/freelance-3d-how-to-determine-an-hourly-rate/