MS Excel 2003

The spreadsheet is for determining the cost for books from a publisher. The
books are priced at a base price plus a price based on the number of
signatures. Pages added in bundles of 12 and these bundles are called
signatures. With 10 signatures or less the price is the base price + $5 per
signature. For more than 10 signatures, the price is base price + $20 per
signature. (The base price of the book already has one signature)

Where C2 is the number of signatures and B10 is the base price, here is the
equation I came up with:

=(B10+(C2-1)*5)

Is there an IF command I can add to this to make it work for signatures above
10? I'm losing sleep over this so any help is appreciated. Does anyone else
stay up until 2 AM trying to figure things out?