Found a formula online in someone's blog for a cheap sanding sealer alternative using MEK and styrofoam peanuts. Think liquid plastic, like Flecto Varathane. Dissolve the peanuts in the MEK to saturation. It should be the consistency of thin honey. Brush on with a disposable brush, sand down after dry. Generally one coat should do it.

Caution: there are two kind of peanuts being used as packing material. The soy based product will not work. But it's easy to spot from the styrofoam.