The cost of mobile home park lots vary, but in resident owned parks are fairly reasonable. If the residents actually own their spaces, monthly "maintenance" fees, etc. could be as low as just over $300 per month. If they are owned by a non-profit, rents could be around $675 a month or so. It really depends on what they are calling "ownership". Whether the listed price includes the spot varies also. I have seen it both ways just in one town. The best thing to do is just ask, and ask if the space rent, or maintenance fees, or what ever they are calling it will be the same to the new buyer. Many of the parks are co-ops, which is another form of ownership.
All you can do is be very vigilant in your due diligence to truly understand what you're getting into.