I don't know of any analog to E1 but there may be another solution:
You may be able to get a 2000 per node and populate it with LS/GS cards.
Each card holds 8 trunks and each cab hold 16 cards.
So you'd need 2 cabs and 25 cards. It would be a lot cleaner than ASUs and I think the LS/GS cards can be picked up on the used market pretty easily.
I'm forgetting at this point, though, if the MXe will take a per node or not.
Ralph