Assuming your locale has no requirement for foundation at depth - i.e. slab-on-grade is allowed, normally about $7-10/SF in lower cost areas like yours. Plus probably $200-400 for the tiedown anchors and straps, depending on whether your area allows tiedowns direct to a slab or requires use of earth anchors regardless - varies by area.
Also - I assumed a 4" slab - if used for uplift resistance also might be required to be 5-6 inch thick, in which case more like $9-12/SF for the slab.
And yes, that does make it real property - which changes taxation in some areas, and also is not allowed in some areas zoned for "portable" trailers only like some trailer parks are.
Cost wise, concrete pedestals to support the trailer and screw anchors and strap or cable ties will be far cheaper than a concrete slab. Be sure, if possibly you will ever sell this unit in-place, to get the tie-down and suport system to meet the federal mobile/ manufacturaerd home tiedown standard so come sale time it does not become a no-go for VA, FHA, HUD, FNMA, GNMA and so forth loan buyers. Also, many lenders even not using federal loans require adherence to the federal standard to protect their loan investment.
Here are a couple of links to references on tiedown requirements for federal loaned units, and typical block foundation costs for mobile/manufactured homes FYI - (I can't vouch for their currency - check HUD or FHA website for current edition -
http://wchapa.org/wp-content/uploads/...
http://www.foremost.com/mygreathome/m...
https://answers.angieslist.com/how-co...
https://answers.angieslist.com/how-co...
