We can do this for you without a problem in Lincoln. The trick is making sure they are nice and tight.
Are they new or old threads? Do you have a stay tap?
As an example for price, we have just done 150 x 7/8" x 6" long stays and it comes out at about £5 per stay. That's in EN3B which certs. Material price is the variable at the moment.
www.jubbengineering.com