My old IBM PC had a monitor which also had RCA plugs in the back. I used that monitor for my Genesis/32x back in the day. Nowadays, I have no clue how that was done. I do wish I still had that monitor though.
So I guess my advice is hit the junk stores looking for ancient pc's and look at the back of the monitors for RCA plugs.
I have an old commidore monitor that also has rca plugs...I still use it as a back up for my consoles...I think it has RGB inputs as well...so I could use it as an arcade monitor too.
My question to you is: Why not use a 13" TV? I'm pretty sure you could find one cheap or free. If you want a bigger Bartop use a 19" or 20" TV. Most likely any TV you picked up would be cheaper than the converter from the link above.
I've looked for the same device in order to use a cheap 19 or 20" LCD monitor with my Plug and play. This is the most inexpensive one I've seen. Usually they are $80 or more.
Expect VCR quality Video.