Through tickets with guaranteed connections are offered by Amtrak right now. I ran POR-NHV for next Wednesday and got multiple options with coach fares ranging from $60 to $85 using all-rail options. The variances would be the result of available inventory and yield management. The itinerary assumes the connection is a self transfer, BON-BBY. Of course, there wouldn't be a problem boarding at BOS with a BBY ticket.
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Note the "20 minutes" is the estimated time required for transit itself. The actual time between arrival and departure is 60 minutes between trains, but I cannot seem to get that to show on a single page.