Instrumentation and Online Stores

You might find it easier if you separate the spec sheets and pricing.
Vendors will always be very circumspect about handing out pricing
information. Even going through users and finding out prices of equipment
that has been already been purchased is unlikely to be successful, pricing
information is generally held commercial-in-confidence by all parties.

Spec sheets should be easier to come by. ISA have them for basic
instrumentation items such as valves and thermowells. Companies that do
instrumentation design sometimes use ISA ones, or have their own, you could
try contacting design offices, companies like Kellogg and Hatch.