We've already put money out of pocket for this project (ie. earnest money deposit on land offer, soil/perk test, paid builder to dig hole for perk test, etc).

Has there been erosion of the soil under the foundation and will that need to be stabilized?

Sandy area as well is doing pretty well for higher market rents with less stipulations.

@Tim Kaminski Some of the deck renew procucts have a sandy texture.

Besides that with basically every home built prior to 1980 will have some foundation issues because of the clay soil here in Texas, it's a given to allocate for problems. 

We have cruddy clay soil that moves constantly and causes all sorts of issues with the slab foundations, resulting sheetrock cracks, etc. 

Jon here it is what we had install in the past626-003 Torrent- warm sand is 80c/sqCarpet Pad/traffic master pad alb 49c/sq

Kitchen and bath wet areas.Flushing areas.Window and door seals.Around all penetrations (hose, faucets, duct work from vents, fireplace and chimney vents).Vinyl, aluminum or wood siding.Stucco or mortar cracks.Interior settling or shrinkage sheetrock cracks.If you have a basement and it has a sump pump, check to make sure it is operating properly, clean the pump screen and remove any soil buildup from the well.Clean and repair gutters.

I posted an ad, say 80' long 10" deep trench of mostly sandy soil and for them to give a quote by email.  

Your survey company is supposed to give a topographic survey telling you what the current elevation of the ground is, and then an engineer is to test your soil to tell you what you're building on.