Add setting for pricing level

Issue Summary

It's great to be able to charge per term. In some instances, it would be very useful to be able to have different pricing level. Such as "Premium" "feature" "regular" (created from CCK). For instance, when "Premium" is selected, this would add $5 to the publication cost, and Feature would add $3.

OR an alternative would be just a box to add any amount to the default publication cost. Basically the "View" would be that the highest amount will show first, almost like a bid node display.