You should get the achievement whilst playing offline, but if you didn't it may be glitched. It has been reported that afew achievements can glitch on Red Dead Redemption so.... You can just start a new save though and you should have £70 in no time, then you can head over to Thieves Landing and buy it. You don't have to wear the suit to obtain the achievement.
No
You can get 43 achievements offline on halo 3 im not sure on odst.
I am sorry but there is no offline co-op
no only online
you cant
no
No there isn't and it is extremely unlikely that there will be
no it is on online mode
yes, you can have up to 4 players offline
you cant. until dlc comes out.
Most likely because there is something wrong with your disk or console
You cannot play multiplayer mode without internet connections.