D.C., Thanks for the help and sorry for the delay in replying, I've been busy and ill :-)

I actually want to obtain the force, in PSI, applied to a board between two plates pressed together by the jack.

Normally the way this is done is by obtaining the pressure exerted on the ram and calculating the force on the board from the CSAs of the ram and board (and possibly return spring but I don't know if this will be significant until I experiment a bit).
There are several ways of doing it, but I was hoping to keep the ram/pressure sensor part under £70 because I know that this should be achievable (i.e. I can get a sensor for £25 and I know there are jacks with ports out there for around £30 quid I just can't get them to me for less than £70 :-) but there's always the DIY tap option so the < £70 is still viable).

BTW, I'm 90% sure that someone here has found me a hydraulic press with gauge tap for about the price I was hoping for :-)

Anyway, I hope everyone had a Merry Christmas and I wish you all Great New Year!