What kind of home is this? Single wide / size / age?
How does the home you can by for $7k compare to the comps your seeing for $30k? Are they truly comps? Would it require any updates or improvements etc?
On the new park side - is the lot set up for a home like this? Does it require any foundation/concrete work? Electric service up to date? Will the park cover the cost of these if they need to be updated? Will it require new skirting?
Most parks love for someone to move a home in - some will even pay for the move. If its a park in high demand, that's probably not the case though. A lot of times, the cost to move a home from one park to another is just not worth the effort. By the time you add up the expenses to move it, like you listed, plus improvements it may not be much more to just purchase one already there or even buy a new one. A lot of parks have relationships with MH manufactures and can bring homes in pretty affordably. But - heck, it may make sense. Hard to say without more info.