Look at
www.backscatter.com and then look at what they have under Compact Cameras. When looking at strobes remember you have to include the optical cable too, and some kind of tray with connectors to hold the strobe. If you want to stay all inclusive in your $500 budget, there is a Sea & Sea YS-03 kit, which has the strobe, cable, tray and flex arm for $479.00. The YS-03 is a good basic strobe but it only shoots in TTL, there is no manual setting. The Inon S-2000 is $365, a better strobe but you would need everything else. The Backscatter MF-1 is on sale right now for $350. It looks like a good strobe for macro, with a lot of adaptability. I've never used it but I assume it is the same quality as other Backscatter products, which I do use. With regards to a light ring, probably not the best option yet. I have a light ring, love it for macro but it is much more limiting then a strobe. Save it for a B-Day, Anniversary or future Christmas present.
Just as an FYI, I use a TG-6, in an Olympus case with Sea & Sea YS-01 strobes. They are an upgrade form the YS-03 but at a cost. I've been happy with them and I get good results in both Manual and TTL modes. There is a learning curve for them, just FYI. Hope this helps. Look at Backscatter though, lots of good stuff for the TG-6 and some great videos.