I think I can help you out, I have been running my starter rig for a couple years and I did a lot of research.
Recorder
The jb3 is a good idea because of the ease of transferring to computer to be burned to CD, which is what I'm assuming you want to do. Even with the slight compression and cheaper price of MD, you would still be able to make a quality tape just as good as the jb3. Where MD becomes inferior is that you would have to buy a MD deck and a digital soundcard for the digital transfer as caymanreview previously pointed out. Find a way to get a refurbished jb3 in your rig and you won't regret it.
Mics
because you're stealthing in a Metallica concert, you're going to have to avoid omni-directional mics because they would pick up too much crowd noise and some cardioids or hypercardioids will not eliminate the problem but help it. These are the very mics I bought and for your budget I would highly recommend them:
http://www.soundprofessionals.com/cgi-bin/gold/category.cgi?category=120&item=SP-CMC-2&type=storeThose are the Sound Professionals at831 (sp-cmc-2) cardioid mics. Very similiar to the before mentioned at853's in that the at853's have interchangeable caps (can switch from omni to cardioid or hypercardiod) but the cost is $50 more. Either set will work.
Mic power
You will need a battery box for those mics for sure, I have one as does a majority of tapers who run such a setup. You can find one at the same site:
http://www.soundprofessionals.com/cgi-bin/gold/category.cgi?category=310&item=SP-SPSB-1&type=storeYou essentially could get the bare batt box with no additional features (that cost more) but if there's one feature that would benefit you most it's the bass roll-off option ($20). If you can afford it definitely get the preamp option ($140 + level control[$20/30]) but it's not absolutely necessary.
This can be your basic rig. I'm also assuming the jb3 has a line input. I haven't used one, I went the MD rig as the jb3 was not available at the time. can someone please confirm this? If you have any questions just pm or email me.