Is there a floor on this? Splitting 10 acres into two 5s doesn't seem worth the paperwork

Your comps might be fine. The problem is that most of your cost base doesn't shrink when the deal does. Boundary survey, mylar, recording, attorney review, the trip to the planning commission, those all cost roughly the same whether you're creating two lots or eight. On a two-lot split you're spreading maybe $6k to $10k of fixed cost over two sales. On an eight-lot split the same base is under $1,500 a lot. That's why people talk about a floor. It isn't acreage, it's how many lots you can spread the fixed costs across.

Also somebody has to mow the unsold half and it will not be the county.

Check the minimum lot size before you check the comps, because it can eat the whole idea. I looked at a piece where the zoning said 5 acre minimum and I thought fine, two lots. Then the health department said each lot needs a primary and a reserve septic area with passing soils, and half the tract was hydric. One of my two lots was a lot on paper and unbuildable in practice. A perc test runs a few hundred dollars per site in most counties and it's the cheapest way to find out you have no deal.

The thing that caps me at this size isn't the paperwork, it's that the buyer pool for a 5 acre lot in a rural township is thin and seasonal. Two lots means two separate waits. Where I've seen the math open up is going from a 10 acre split to something like 40 acres into eight 5s, because then you're advertising an inventory instead of a listing, and you can price the first two under the comp to get momentum and hold the last two firm. On two lots you have no ability to do that at all. Flint, what's the actual days-on-market on those $28k comps? If it's over 200 your carry is where the margin went.