Even if you can't buy everything off the MB, snagging an ilvl380 weapon off of there would help a lot, as weapons tend to be the hardest gear to upgrade. Not sure what they're running for on Cerberus currently, but I usually see them going for 50k or less, which should still leave you plenty of gil left over (and running roulettes will help build that back up relatively quickly). Just make sure it's High Quality - look for a glow to the weapon's appearance and a little HQ marker next to its name.
