i've noticed that myself. i just begrudge paying £20 a book when i paid about 10 for These Haunted Seas and don't see why they couldn't re-release the second. i know about the lack of sales etc but it's not very good on pocket books part i don't think
Pocket Books should deliberately release a huge trade paperback that they
know, due to disappointing sales on the first two, will be difficult to make money back on their investment?
Even when MMPB "Mission Gamma" books were going for $80+ in the online secondhnd market, I was seeing bricks 'n' mortar bookshops with copies of Books 1 & 2 on their shelves
at regular prices, and second hand ones for less. At the time, IIRC, Books 3 & 4 were still "in print" at Pocket, and they only went out of print because new people, finding the omnibuses for the first time, exhausted the Pocket warehouse.
Now that demand is for Books 3 & 4 instead, I'm again seeing bookshops with copies on their shelves at regular prices. So keep looking, or try the eBook versions to satisfy your hunger - and then pick up actual copies when you see them at a reasonable price. Remember that Pocket made many more copies of Books 2-4 in MMPB because sales of MG #1 were so solid. (For a long time, it was only Book 1 that was "hard to find" - partly because there were less copies printed.)