Ok, I looked and .40 to 9mm conversion barrel is $209. And that's probably a very fair price considering what goes into making a barrel. I haven't checked the market in used Shields, but new ones can be had for around $330. Probably you can find a used one in good shape for $300 or less. You can probably figure where this is leading. You need a 9mm magazine or two to go with the barrel. I know some say that you can use the .40 mag, any maybe so for RANGE duty. But not for carry, at least
I wouldn't. Add another $60-70 or so. I have a .40 Shield that I'd like to have a conversation barrel for. However, I doubt I'll be a customer for one of these.