Welcome to skoolie.net. If you want more from the site than just a welder recommendation, click User CP in the upper left and edit your details, then people here will know where you're at and what kind of bus you have.
Your floor looks somewhat familiar, as I had to rebuild the same floor area in my bus. You can check out my build thread for details; here's more of a summary of the floor rebuild: https://imgur.com/a/Vp4Xpv6
What you have there looks good and solid. I have no doubt you could pick up a cheap Mig welder and weld on the sheet yourself, after a little bit of practice. Or at the very least, you could tack things together and then drive to a welder to do it up fully (way cheaper than mobile welders).