It's worth asking around to see if anyone's getting rid of their shooting frames. I got mine for a tenner off some old boy who was about to pop his clogs, and the lens cost about Â£20 from the opticians. Job jobbed!
It's OK, so long as they fit perfectly. It also depends what kind of TR. More likely for fullbore than smallbore, I'd have thought (you spend less time in the aim).
I wear contacts, but I don't use them when shooting; I just like perfect vision in the sight picture (not almost-perfect), and I'm willing to trade off peripheral vision to get it - a big glass lens can be made more accurate than a high-water-content piece of plastic.
The other problem is the slight delay after every blink before the lens settles back into position; I find it quite annoying, as it interferes with my shot routine... if I've got the perfect position and wind condition, I want to take the shot now, not in a second's time while I wait for a sight picture.
I know two Commonwealth medallists who use lenses for SB TR, but they had to work with a sports vision specialist to get it just right, i.e. minimising the settling period after a blink. I also think that they use gas-permeable (i.e. fairly rigid) lenses.
One piece of advice if you decide to get a set of shooting frames - get a "pistol" lens holder (the 42mm diameter frame) and not a "rifle" lens holder (about half that diameter). It gives you acceptable peripheral vision, assuming like me you're a bit bat as a blind (about 2 diopters of correction)...
If money is genuinely no object, get a pair of these - there are various UK distributors (note to the sceptical - they allow you to place the lens exactly perpendicular to the line of sight, however you've put your cheek on the cheekpiece - a bit like that snooker player whose glasses looked a bit daft, but let him look "upwards".)
There's more than one reason why wearing glasses is a good idea.
Personally I use the ESS ICE 2.4 with prescription inserts. This is the same as the in-service Lightweight Ballistic Protection. It's an issue item if you are deploying. Full details in the sticky in the QM's.