My suggestion - create two plans for each platform (if you use Win and Lin*x):
1/ Basic plan with just webspace and email (no extras like databases or webstats, etc)
2/ Business Plan with most of the features you want to support (still limit the numbers - for ex.5 databases, 1GB of bandwidth...)
Make the Basic plan really cheap, and price the options realistically, still - if they add the options they would pay more than the Business Plan. This way you'll give them the ability to start low, and then expand/upgrade when needed.
Drop me a line if you get stuck: klokany*at*yahoo.com.au