My custodian just asked for a fair market value on the Missouri land and I have no idea what number to give them

A qualified appraisal from a licensed appraiser is the defensible standard, but most custodians will accept a broker price opinion from a licensed agent or broker who can show their comparable sales methodology in writing. County assessed value alone almost never satisfies the requirement because assessors in rural Missouri counties frequently run 60 to 80 percent of market and custodians know it, so if you submit that number without a professional signature behind it, expect a pushback letter.

The cost risk on an $18,675 asset is real and worth naming clearly. If an appraisal runs $400 to $600 annually, you are paying two to three percent of the asset's value just to hold it in the account, and that drag compounds over a long hold on raw land that produces zero income inside the IRA. A BPO from a rural land specialist typically runs $150 to $250, and if your custodian's acceptance policy allows it in writing, that is the number to push toward.

The assumption doing the most work in your situation is that the custodian's written policy matches what their compliance department actually accepts when reviewed, so I would call and ask them specifically whether a signed BPO from a licensed Missouri broker counts as sufficient documentation before you spend anything. What does their letter say exactly when it describes "documentation," because the specific language there tells you how much room you have?

The annual valuation requirement is real and the stakes are worth understanding. The IRS requires SDIRA custodians to report fair market value on Form 5498 each year. That form goes to the IRS and is part of the compliance record for your account. A number you made up without support is the kind of thing that creates problems if the account is ever examined, so you are right to take this seriously.

Here is what custodians typically accept for raw land, roughly in order from strongest to cheapest:

Certified appraisal. The gold standard. A licensed appraiser researches comparable sales, adjusts for differences, and signs off on a value. Appraisers who work rural and agricultural land in Missouri exist and can usually do this for $300 to $600 depending on complexity. On an $18,675 asset that is a real bite, but some investors rotate appraisals every two or three years and use cheaper documentation in between.

Broker price opinion (BPO). A licensed real estate broker signs a letter stating their opinion of value with the reasoning behind it. Many custodians accept this. Cost is often $100 to $250. Call your custodian before you order one and confirm they will accept it, because acceptance varies.

County assessed value with a multiplier. Missouri assesses agricultural land at a fraction of market value, so the assessed value alone understates it. Some investors submit the county record plus a written explanation noting the assessment ratio for the county. Some custodians accept this for low-value raw land, others want professional sign-off. Again, ask your custodian first.

The thing worth knowing that you did not ask: whatever value you submit becomes the basis for calculating your required minimum distributions later and shows up in IRS records. Consistently low values look favorable now but can create a mismatch when you eventually sell. A defensible, documented number protects you in both directions.

What did your custodian letter specify as acceptable documentation formats?

County assessed value alone will almost certainly not satisfy a serious custodian, because Missouri assessment ratios are set by statute for tax purposes and bear no reliable relationship to market value, and the custodian's compliance team knows that. A broker price opinion from a licensed Missouri real estate agent who can pull deed transfers in Adair County and adjacent counties, weight them by acreage and road access, and sign a one-page letter on company letterhead is the middle path most custodians accept for raw land under roughly $50,000, and it typically runs $75 to $200 per year rather than a full appraisal fee. The documentation you attach matters as much as the number itself: the BPO letter, the comps the agent used, and a brief note explaining why any adjustments were made gives the custodian something defensible if the IRS ever scrutinizes the valuation. A full USPAP-compliant appraisal becomes the cleaner answer if the value swings materially, if you plan a transaction inside the IRA involving that parcel, or if the asset grows large enough that a few hundred dollars in appraisal cost stops mattering against basis.

The question I would put to your custodian directly, before you spend anything, is whether they publish an approved documentation list for illiquid assets, because some custodians will name the BPO explicitly and others will only accept a licensed appraiser's signature, and you want that answer in writing before you submit the form.