Yeah, Exodus' purchase files are screwed up this build. For whatever reason, all the Mech and Pilot entries after mission one have a "//" in front of them, which means they aren't available for purchase. A side effect of this is that the game no longer reads the components tab correctly either, so none of the components that are listed are for sale either, even though they're listed correctly. It's an easy enough fix, just go to the campaign file, which is in the data/campaign in your MCO install, use that to determine which purchase files are used by the missions you're playing, and fix them accordingly. All you have to do is remove the "//"s from the front of all the Mech and Pilot entries - not the ones after, though. Those are part of the file names.
The purchase files are all located in the data/missions, and they're .fits, so they can be read with Wordpad. Editing them is nothing. If worse comes to worse though, there's a purchase file tool that comes bundled with MCO, so you can use that to generate your own if need be. Just make sure to label them correctly in the campaign file.
It doesn't look like any other campaigns have this issue, thankfully. It could also be a conscious decision on the part of the MCO team, in order to make Exodus harder, though considering how spotty salvage can be in this campaign, I totally get how this can be annoying.