my library doesn't have books 1-3 or 5, so its not like I had a choice
Erm, you could buy the books?
There are no bookstores near where I live, I could only get them from Amazon. I won't pay more than about $5 for a paperback book (or any book, with the exception of things like tech books like Mr. Scott's guide to the Enterprise, which I got for less than $5 with shipping but probably would have shelled out a few more dollars for if I had been forced to), and to get me to pay $3-5 those have to be great books. Amazon charges $4 in shipping, so a book would have to be amazing, and about $1 used for me to consider buying it from them (I never buy new, unless its a great deal compared to the used copies of something, which it almost never is). Since the stuff about the Typhon Pact really isn't hard to follow or get caught up on by reading the other books, I would never even consider buying the older TP books.
I probably have almost 100 ST books, but I didn't pay over $2 for any of them. Second hand stores and other sales have been very good to me, and I've gotten great deals (like getting the first Star Trek Encyclopedia and the hardcover Updated and expanded edition at different times for $1 each). I've bought one paperback novel from Amazon, book 2 of the Star Wars Republic Commando series. Its my favorite SW book series, and the library has lost 4 of the books and never replaced them. Its probably in my top 5 book series ever, so the book warrented the price (as will books 3-5 when I buy them). Off the top of my head, as much as I love ST, there is no book the library or I don't have that I want to read so badly I'd pay $5+ for (although if the library lost them I'd definately buy the Department of Temporal Investigations books and Q-Squared, in fact they may get purchased eventually anyway) atleast as long as the Library is still buying most of the newer books. I would like to read a lot of the newer Voyager books, which the library doesn't have, but I'm not willing to pay what they cost at this point. I know I'm missing some interesting stuff, like the last Borg invasion that keeps getting mentioned and why they aren't around anymore, or why a trill counselour is in command of a starship (Seriously, Ezri gets a ship? Who gets one next, Bashir? Nog? Are they just handing them out now?) but paying more than $1-2 for a book just isn't something I like doing unless I absolutely have to. Thats not to say there aren't some awesome Star Trek books out there that I don't own and that the library doesn't have. I just have a certain price I'm willing to pay for books, and since I don't have a lot of money I have to ge selective with what I buy.
As for what I'm reading, I finished book 2 of ST - Cold Equations. I'm reading book 3, then I'll go on to Brinkmanship, then Star Wars - Scoundrels or Star trek - Allegiance in Exile, depending on which one I get from the library first.