There are two costs worth planning for, and they're both smaller than people expect.
Drafting is the first. An attorney preparing a promissory note and a deed of trust or mortgage for a straightforward single family sale is commonly a few hundred to a couple thousand dollars depending on your state and how much negotiating goes into the terms. If your terms are unusual, a balloon, a step-up rate, a release schedule on multiple parcels, it climbs. Get the quote in writing before you start, and confirm what's included, because recording fees at the county are separate and small.
The second is loan servicing. A third-party servicer collects the payment, splits it into principal and interest, tracks the balance, handles the year-end interest statement, and often escrows taxes and insurance. Typical pricing sits in the range of roughly fifteen to forty dollars a month for a single note, sometimes with a setup fee. Compared with doing it yourself, you're buying a neutral record of who paid what and when, which matters enormously if you ever have to prove default. A spreadsheet you maintained yourself is a weaker exhibit than a servicer's ledger.
The thing that trips up sellers doing their own collection is not the arithmetic. It's insurance. You want to be named as mortgagee on the buyer's hazard policy so the carrier notifies you if the policy lapses or if there's a claim check. Otherwise the house burns, the buyer takes the settlement, stops paying, and your security is a vacant lot. A servicer will usually track that lapse notice for you as part of the monthly fee.
