How much would custom build strat pickups made to fit a 5/6 string cost

[dlmarquez]

Not sure on spacing, but the Lipstick pickups might suit your requirments

 

[Ritter667]

You could use 2 Strat pickups, and make one split coil pickup out of it, like P bass, but with the two halves being 1 single Strat pickup each.

An idea I have been toying with myself.

Pole alignment won't matter in that case, but you could also always get blade/rail style strat pickups.