we're in the process of this nw (need to update my original sheep-licks thread about it).
Soil samples cost £19 per field for the broad spectrum tests (pH, NPK, Copper Sulpher.... those sorts of things) and about £39 per field forthe full-on animal health testing package - cobalt, selenium, etc etc, pluc broad spectrum.
We have 30 sheep, and probably double that number of breeding ewes once we're at full capacity. We've decided it's worth doing as it suits our desire to have a ver low-input system where no food is bought onto the holding frm outside. This is probably only possible if the soil has the right minerals in it, and then if those minerals are carried through into the grass and hay crop. We'll test the hay crop in the summer once it's made.
We've had the results back from 2 of our fields so far, broad spectrum only... others should be back the end of the week. We've been told that NPK are in the regions that are fine for grazing land, but that the PH is too high. We kind of knew this anyway. we've got ph's of 5.3 and 5.6 in these 2 fields. 1 tonne of lime per acre was recommended as a start. We've made sure that any lime this company source is local (which it is), and we're going to do some sort of wildflower/plant assessment before changing any of the soil chemistry.
As far as companies go, I don't know any in your area, but your local farm-factor will point you in the right direction. It's Mole Valley farmers down here, but I would guess you'd have a countrywide stores or something like that in your area? facebook is a good source of contacts too... is there a farmers free ad's suffolk group?
HTH