Technically, you should get an appraisal as to the fair market value on the date of death.
If the prices in the particular area have not changed to any extent, you can try using the sales price as the basis but, if audited, you will need to justify the basis (e.g,, with documentation).
Note that the six month alternate valuation date is only applicable in certain instances. In short, it applies to rather large estates and even then, only if the alternate valuation reduces the size of the estate and the amount of estate tax due.
