I would be cautious towards such items as with any communication, a dropped character can prove to be dangerous for the operator as well as costly on material or machine.
Most RS232 to wireless adapters are going to run you $250+ that are reliable, proven and problem free.
We found units for $99 bucks but resetting them nightly to make work seemed to be a waste of time. Furthermore, units that only support Fanuc controls are limited, and may not be feasible for the future.
We have options on our website that you might consider.
Greg Mercurio -Shop Floor Automations
www.shopfloorautomations.com /619-461-4000