The other issue to consider is that a trailer will depreciate in a good market while a house retains its value or increases. Once a trailer gets to be a few years old financing on it could be a real problem. I have read past 5 years it is difficult. Past 15 is almost impossible. Confirm with a lender near you.
If you do put a trailer on a lot (why not) a concrete pad instead of gravel will stop a lot of settling issues. It also costs more. I would also seriously consider a doublewide instead of the standard 14 x 70 trailer. It is not much more expensive and gives a lot more useable room. Think of a 14 x 80 trailer. Cut it in half, place the 2 parts next to each other and you have a 28 x 40 for the same price. It does take more work to put together on your lot and it has 2 times the shipping costs. That means it costs a bit more but it is a lot nicer home to live in.
A 16' wide trailer is also very nice. It is not even comparable to a 14' wide one. It feels so spacious compared. You can even find used double-wides and foreclosed double-wides and regular trailers the same as houses. Check for the type of quality they were built with.
Find out how much it costs to buy a lot. Now add in water and sewer (city hookup or your own) electric wires from the utility to the trailer and a driveway. That is the real cost of a lot.
You can also go to a mobile home dealer and ask about a land contract. Up here they have house lots already to move your trailer onto and will sell a package deal. Or at least they will put it together in time for you.
Before you do buy run the numbers. See if it makes more financial sense to rent or to buy. I would not mind paying an extra $200 or so a month to own. In time it would be mine. I would have a problem with paying a whole lot more to own as financially it would not be good for me.
The blog below shows the real way to see if it makes sense to buy or to rent. Time frame of ownership also matters.
Some towns and lots have restrictions on the use of mobile homes. Check into that before buying a lot. That way you do not buy and find you can not use it.
I tried to cover what I know of mobile homes here. I hope it helped.