Do something similar to Gears of War 2 with the flashback map pack.
Have a Halo Throwback pack free if you buy the game new or pre-order or 800 points if you get it used.
Map pack would contain:
3 multiplayer maps
Halo CE Map (Prisoner)
Halo 2 map (Lockout)
Halo 3 map (Sandtrap)
1 Firefight map
ODST map (Crater)
3 armory items
Mark V Helmet (early access obtainable later on in the game)
Mark VI Helmet (early access obtainable later on in the game)
SGT Johnson FF voice
Everyone wins this way because the sales boost so more people buy the game to buy future DLC and the customer isn’t shafted with a weak amount of maps.