I seem to recall the price going up after the initial $500 deal, and then again when it went to $400. I think they're just doing these sales about a week at a time to bleed off stock, and if someone buys between the sales, they're happy to take the higher price for them.
As tempting as the $300 sale was, I just couldn't justify a 4th Solo, but I did just pick up two more batteries and a spare gimbal. I wish motor pods were more widely available (at these kind of sale prices), but it seems 3DR either didn't make many, or is holding onto their stock for Site Scan support. Oh well, I think 3 Solos, 4 gimbals and 10 batteries will do me for the foreseeable future!