I can only really afford one dlc and i want the one that will add an ending or allow you to play after end like brother hood of steel any idea?

It's confirmed by the DEV's that there will not be a Broken Steel kind of DLC, sorry bud.

That svcks but i can under stand why. Fallout 3 really had only one ending so it was easy to make where fallout new vegas was like early fallouts there were 4 different out comes. Making a 10$ dlc that shown your choice and outcome like you having army of robots or ncr in control or legion would been hard.

Maybe an expansion for 30$?

There are no post end DLC, This has been said many time before.

Very little detail given about current DLCs planed (well Honest hearts and Old Worlds Blues have some detail)

EDIT: No expansion could cover the shear scope of the changes to happen, would been disabling nearly the entire of the NCR or leigion, stripping the casinos etc... and then theres indvidual endings like goodsprings, prim and companions etc.... based on which main faction wins. to much to chnage and would hamper the game engine whats already on its last set of legs.

Just make a save before the battle of hoovar dam

There might be additional screens and narration added to the ending, that's it

Just wait for a mod. It'll takes months upon months but somebody would make it. Remember that in Fallout 3, some mods were even better than the DLCs themselves.