usually the old head with a dropped valve seat can be rebuilt. they may need some re-welding then new valve seats are installed.
a used head with out the benifit of the seats being replaced correctly may or may not last long before another seat drops. but if you find a used head that would be cheapest. but with all the labour and stuff to install it, if you can afford it, it might be good to have all the seats redone anyways, thus maybe have that done for your head.
of course if your near a place that does a good job at seat replacement you can save shipping charges.
also cheack out teh aircooled VW sites, they can maybe recommend a good VW head rebuilder near you, or offer a source of a replacement used head. these typeIV motors were used in way morte VW's than 914, so there should be a good source of parts, however some tyypeIV heads are different than others, different intake ports/exhasut ports, and in the case of the 2 liter 914 different spark plug holes. so beware about buying anyold typeIV head, be sure you specify it is a 1.8 914 head however any good VW head rebuilder can re-do the valve seats and valve job for you.
good luck in your quest.