Well, there are a few of ways you could do what you are asking:
1) Just put the price as part of the checkbox value along with the domain. Seperate them with some character like "--" and then split the values in your form processing script.
2) When you create the checkbox, create a hidden form field with a known name to hold the cost.
3) Store the costs in a serialized array in a session value that you can retrieve when the form is submitted.
The last would be the smartest thing to do. Never <b>Never</b> <i>Never</i> store prices in forms unless you have some way to verify and validate them in your processing script! It is too easy to save your html source, alter the prices, and then display and submit the form with altered prices and get your services for a buck!
-- HTH
-- Rich