A small campaign, honestly costed, looks like this. Data somewhere between 50 and 300 a month depending on whether you're reading the docket yourself or buying court-sourced filings. Two hundred pieces of mail at roughly 75 cents each is 150. Skip tracing on a couple hundred records is maybe 20 to 40. So 250 to 450 a month for a one or two county effort, and that assumes your own time is free.
The number people miss is duration. Heirs respond on the estate's schedule rather than yours, and a case often has months of creditor notice and accounting to get through before anyone can sign anything. A campaign that runs once teaches you nothing. Six months is the usual minimum before you can tell whether the list is producing, so budget the whole 1,500 to 2,700 up front and treat it as the price of the test.
There are costs outside the mail too. Earnest money of 500 to 1,000 per contract, whatever your state charges for title work or an attorney closing, and the cash or the buyer to actually take the property down when someone says yes. Getting a signature you can't close on is worse than getting none.
On land specifically, the empty parcel has no cleanout, no roof, and no vacancy insurance problem, which removes most of what makes probate houses expensive. Your motivation question is the right one, and the answer sits in whether the heirs have any use for the land at all.