You could try here, they may have something you could buy for cheap.
http://graphicriver.net/category/icons/software
These guys make some nice icons and do custom work. They have some nice stock sets but they are a bit more expensive than the first link.
http://www.professional-icons.com/stock-icon-sets.aspx
A third option would be to go over to
http://www.99designs.com and put up a price, describe what you want and let the proofs flow in.
In my opinion giving you an estimate is kind of tough. If i see something beautiful and I can afford it, ill probably buy it. It depends on how invested personally I am with the project. Probably not the best way to get it done but that's just me lol.
Best of luck