Unfortunately, I think the most cost effective option would be:
-Surface-run the Greenline along 11th Ave.
-Tunnel north under Centre Street
-End the tunnel past 4th Ave
-Build a surface station in Chinatown
-Close the crossing at Centre street and 3rd Ave. to vehicles.
It's a shitty compromise, and building an 800m tunnel with an underground station at 7th Ave is going to be expensive. But at least the city saves money crossing the Bow River by using the Centre street bridge. Without additional funding, I don't think the original plan is going to get off the ground.