Tec #400 = 1st Manbat.
The more expensive books in the runs from a high grade perspective are:
Batman #217 (HTF in high grade), 222 (Beatles swipe), 227 (classic Tec 31 swipe), 232 (1st Ras Al Ghul), 234 (1st BA Two-Face), 243 (black cover), 244 (classic nipples & bat-undies cover), 251 (classic Joker cover)
Tec #395 (1st Adams interiors), 400 (1st Manbat), 402 (green Manbat cover is tough in high grade), 405 (1st league of assassins), 411 (1st Talia)
From a story perspective, the Tec #411/Batman #232,235,240,243-44 Ras Al Ghul story line is the best read IMHO.