So, Holyoke built a 400ft platform station in 2015 for $3.2M, which included parking and a building with restrooms. So, cut out those costs and substitute another 100ft of platform and account for inflation. $5 million? So, do that twice. Add 1000 ft of passer at S. Nashua, upgrade Class 3 to Class 4(CSX wants $500K per mile to upgrade a multi-mile siding for West-East). Let's call that $10M. There's one 40ft bridge on the route, barely worthy of the name. Signaling/ACSES? Let's say $2M per mile, which seems to be the Ts number.
I'm looking at $50M to get to Nashua and build a layover, which the T needs anyway. Rolling stock? Well, if the T gets off it's duff and buys some EMUs for Prov, Stoughton and Fairmount, there will be sufficient existing stock. And don't forget, at least 10 of the 32 runs per day could be done by the existing Lowell trainsets, with the addition of 1-2 cars each.