fanpages: self hosted iframe vs 3rd party service

I want to create Facebook Fan Pages for companies as a business. I don't want to do it forever but I keep seeing how it'll bring in 'easy' money.

The business model is well known and pretty straightforward. Create a Fanpage either before (they buy what they see) or after (you build what they want) contacting the target business and charge them either a flat fee for the design and installation or charge an ongoing fee for the continued hosting of the iframe design.

The trouble for me comes when it's time to move on.
I can either have lots of client fanpages being hosted on my server so I can then either sell/give them the folder that contains the design and bid them farewell..

or..

if I were to use a third party design system (like Wix or 5min fan page or a variety of others) then I'd have a hard time transferring all my clients to that service in order to get out from under.

My main concern is being forever tied to the client. On the other hand I've seen relative few design templates that I can host myself and am drawn to the robust and simple design methods of these third parties.

I'd love to hear/read others thoughts on the matter.

Thanks,
Mike