I think the most expensive items now are Hami O's, purples, and winter IOs, and even then none of those are anywhere near what they were on live (well, I think some Hami O's are going for more, but that's because there's way less supply and PvP builds love their microfilaments). Oddly enough, I've only done minimal toying with the market and have made off with a good chunk of inf just using converters and offloading what I don't need. Of course, I run enough content every day that I'm sitting on thousands of reward merits already so I can probably fund all my own builds without ever touching the market, but I just find it easier.