When I earned this achievement, I saved one Polo mission for last. After I made it to memory sequence 9 (to unlock the last books in Constantinople), I purchased all of the books (had purchased the 4 from Cappadocia during that memory sequence). I then went to complete my last polo mission (Forum of the Ox). As soon as I got that book, the achievement popped-up.
NOTE: This was on a new save game that was created earlier this month, but the new save game was created without the patch, while off-line, so that may or may not be the reason the achievement worked for me this time.
See below the book list for the methods I used to collect money. Following these, I was able to do a pretty smooth run-through of the game (not spending hours farming money or anything like that), and had almost 100,000 Acke more than I needed by the time I reached memory sequence 9.
I have 28 books. I got the book "The Flute Girl" in 2 different missions, from two different locations. This seemed suspicious at first, but it is the same with and without the patch.
Also, On Nature is obtained from Signs and Symbols, Part II, even though it tells you that you picked up The Flute Girl (both are readable in the hideout after this mission, but the Flute Girl book does not appear on the shelf until you complete the Polo Mission Church II). -- Thanks for the info, xjoker2x7
Here are all of the books including where they came from:
In the hideout, starting on the left and continuing clockwise through the room:
Stand
1 Aesop's Fables (Sequence 6, Memory 5 - Signs and Symbols, Part III)
Stand
2 Mission to Constantinople (Sequence 4, Memory 4 - Signs and Symbols, Part I)
Shelf
3 Parallel Lives (Constantinople Bookshop - 7,723)
4 The Odyssey (Constantinople Bookshop - 171)
5 Mu'Allaqat (Constantinople Bookshop - 284)
6 Aeneid (Constantinople Bookshop - 206)
7 Geography (Constantinople Bookshop - 411)
8 The Book of Prophecies (Constantinople Bookshop - 2,737)
Shelf
9 The History of the Kings of Britain (Constantinople Bookshop - 450)
10 Anabasis Alexandri (Constantinople Bookshop - 23,460)
11 Opus Majus (Constantinople Bookshop - 8,309)
12 Heimskringla (Constantinople Bookshop - 1,564)
Shelf
13 The Secret History of the Mongols (Constantinople Bookshop - 21,017)
14 Record of The Grand Historian (Constantinople Bookshop - 37,830)
15 The Golden Ass (Constantinople Bookshop - 3,050)
16 Metamorphoses (Constantinople Bookshop - 7,918)
Shelf
17 The Travels of Marco Polo (Polo Mission - Hippodrome)
18 One Thousand and One Nights (Polo Mission - Galata)
19 The Book of Kings (Polo Mission - Arsenal)
20 Nibelungenlied (Polo Mission - Forum of the Ox)
21 Iliad (Polo Mission - Aqueduct)
22 The Cantebury Tales (Polo Mission - Church I)
23 The Flute Girl (Polo Mission - Church II) (Sequence 5, Memory 5 - Signs and Symbols, Part II)
Shelf
24 Bibliotheca (Cappadocia Bookshop - 107,525)
25 Cronica (Cappadocia Bookshop - 84,123)
Shelf
26 Tirant Lo Blanch (Cappadocia Bookshop - 94,875)
Shelf
27 Digenes Akritas (Cappadocia Bookshop - 65,780)
Stand
28 On Nature (Sequence 5, Memory 5 - Signs and Symbols, Part II - book is obtained, but does not pop-up that you collected it, says you acquired Flute Girl instead)
Book Cost:
Constantinople Total: 115,130 Acke
Cappadocia Total: 352,303 Acke
Grand Total for purchased books: 467,433 Acke
Methods used to earn money:
1) Running everywhere (instead of taking tunnels) with a thief group pick-pocketing for me. (Should be an obvious one, but mentioned earlier by VoodooN88)
2) Collecting bomb ingredients from crafting tables, caches in the streets, looting dead guards... then selling often to Pieri Reis.(good tip mentioned by MCoreBE -- some ingredients sell for a lot of cash)
3) Sending assassin recruits on missions that earned money (instead of the ones that cost money) (I think I saw this mentioned by DragonCrusaderV first)
4) Rebuilding shops and landmarks early on to increase money earned every 20 minutes (not sure anybody needs credit on this one)
5) Hire thief group, then climb over the wall of the Mercenary HQ (don't go through the door, or you will lose your thief group). From there, you can fist-fight and bet money, but your thief group will help you, and they have knives! Guaranteed win every time. (I stumbled on this one myself)
6) Save your money... don't bother buying any extra weapons (except the crossbow), don't buy ammunition -- loot dead guards to re-stock, avoid using bombs when you can -- selling the ingredients is a big money booster
7) Hire a thief group, find a place with a lot of people around, throw money or a pyrite bomb to lure everyone close together, then walk your thief group into the crowd -- just a little quicker way to loot the crowd -- only worth it if there are a LOT of people around