Ifrits Cauldron is probably your best bet, I've gone to mine there 3 times, but all I ever got was some ash and sulfur. I used my Ninja with Tonko and Silent oils, then when I was done I was use my 2 hours and ghetto warp back. Its not easy though, I printed out some maps and was all set to go, when I arrive, almost none of the mine points were around, flame spouts blocked off various areas, and most points were close to a bomb. I lost gil in that venture.
Best place IMO is the grotto, if you got good blacksmithing and goldsmithing skills you can turn all those iron ores you get into ingots and keep mining with space in your inventory. Sometimes you'll strike it rich, I made 40k in one venture that lasted like 20 minutes, got lucky with darksteel and gold ores. Sometimes it won't be so good, flint stones and such, but you almost break even.
Go to Mystery Tour FFXI page and look up the sections there, I was about to start mining again, you could probably make your own pickaxes cheap, and most of the ingot recipes require either smithing or goldsmithing to be in the 13-20 range.
Its a great place honestly, if you can craft and have some patience. Just try to go in hours when no one is around. Be careful at level 29, some things can still aggro you, have a map ready, theres 3 places you can zone out, so things shouldn't get too hard.