The SmartTrack program is expensive, but it's scope is also a lot more than just five GO stations.
off the top of my head, it includes:
- Broadview Avenue extension south to Lakeshore and associated grade separation
- St. Clair West road expansions, including the widening of the St. Clair underpass, Gunns Road extension and underpass, and Davenport Road extension
- Finch Avenue grade separation
These elements alone are probably over 1/3 of the cost and strictly speaking are more so roads projects than transit stations.
East Harbour is also a pretty large station in scope. It'll be the second or third busiest GO station in the network upon completion, it's not a regular old GO station with 2 platforms and a canopy.
Bloor-Lansdowne is the only station which is really a "normal" station with minimal additional procurement or elements.