To keep all three of Rundblad, Summers and Stone on the roster the rest of the way would cost only about $650k. I know the Coyotes are on a budget, but Maloney was open to adding a player or two at the deadline, so I suspect there's still some room, and it doesn't serve Maloney to not spend to the budget. Plus, with how fragile this D corps can be, having the depth available isn't a bad thing.
My napkin math says it's an extra $316k as of today. 27 days remaining of 185 in the regular season, and you still had to pay their AHL salaries anyways, so take the delta between NHL and AHL salary.