They were never cheap, I got good money for my setup the other week http://www.ebay.co.uk/itm/2511021264... 4.m1559.l2649
On my Class B buke I used a Stack tacho, I bet a Spa Tacho would also work OK
as do the Scitsu (Red back, must dig mine out and give it a charge). Not sure if an Elliot Tacho will and if so which one.
But there are a host of Digital ones out there these days for just under £100 that will probably work.
Time to find out what others are using