220V to 110V converter

I think you could just come off one side of the 220 . 220 is just two 110's on the hot side .
a converter changes AC to DC . A Inverter changes DC to AC .

Nay verily, I proclaim. If the "220" power in the garage is your typical single phase 240v welder circuit there will be no neutral conductor and thus, no code compliant/safe return path for a 120v load.

I have a standard 50 amp 220V socket that I have used just for my miller mig welder. My garage is the typical garage that was built in the 50's that came with just two 15 amp 110V plugs. I would love to have a converter that i can then wire some extra 110V sockets. What would you recommend?

If you want to break some 120v power off the existing 240v receptacle you would need a small transformer to derive a neutral, which would be cost prohibitive to purchase and install properly. A 240v single phase 50a receptacle will be a NEMA 6-50R and will only have 3 prongs. If this is what you have then chances are there is no neutral conductor. A 50 amp 120/240v single phase receptacle with neutral would be a NEMA 14-50R and will have 4 prongs. Considering most welders use single phase power in either 200/230/460 volts, I'd be really surprised if there was a neutral available at that plug.

Just pay a sparky to run a couple extra 120v circuits to the gayrage. It's your best bet...