Have looked at zope.org solutions providers...... http://zope.org/Resources/ZSP lists a lot of solutions providers and here is one http://www.interlix.com/Plone/Services/WebHosting/
and i think they will allow you to split the hosting plan and be able host multiple domains in the plan according the person i spoke with in interlix support.... Give them a call and get more definitive answer.... and by no means i suggesting only interlix there maybe other on the zope solutions provider list....try filtering them and hope you find the best....
Disclaimer: I am not responsible for anything that happens to you..
I have been reselling from networkeleven.com... they support python and i asked if plone and zope were available and you can install it into your site(s).
Networkeleven is probably the best company I have dealt with. Price is a little higher than others, however, the service is by far the best I have ever seen PERIOD. They are on a fast backbone and people are easy to get a hold of via phone and helpdesk. The freely upgrade their plans to compete in the market place when they see a need, as my plan has already doubled in space and bandwith yet not 1 dime I have had to pay extra. Never had a problem with Cpanel there and they don't touch their machines unless they have it scheduled. Absolutely the best I have dealt with + plone/zope support.