Edmund optics sells lens elements that you can buy coated or uncoated, priced as follows for a 100mm fl/30mm dia/PCX:

$30.40 no coating
$33.20 MgF coating
$34.70 "Vis 0" 0.4% coating

Overlooking they are charging $30 for a $3 lens, coating seems to be around $2/surface.

An on-line discount eyeglass firm charges $6.95 for AR/no scratch coating, again around $2/surface.
Admittedly, a High Street optician will soak you for $80 for the same service.

Coating pricing is _very_ screwy.