There are a lot of options and iterations that they can do for the rest of the season. Here is what I see in the most simplified way that I can come up with.
Tax Limit: $187,895,000
Current*: $187,257,831
Under Tax: $637,169
*Includes the 12 regular contracts plus the (2) 10-day deals for Tonje and Banton.
The 10-day deals expire I believe on March 1. They then have 14 more days where they can be under 14 contracts. That gets to March 15 with 28 days remaining in the season. By this date, BOS needs to sign (2) more players to get back to 14, either 10-day deals or "rest of season" deals.
If they simply signed Tonje and Banton to "rest of season" deals on March 15, the cost for each would be:
Tonje: $204,830
Banton: $369,515
Total: $574,345
Remaining: $62,824
That would allow them to sign pretty much anyone they wanted to a last day of the season min contract. That could be Shulga or Harper, but wouldn't have to be. If a more tenured vet were to become available, even a 10+ year vet, there is enough money to sign that player as well. And as someone said, this could be a multi-year deal, it doesn't have to be only the rest of this season.
Since they have chosen to sign Tonje and Banton to these first 10-day deals, I am not sure why they would chose a different player for the rest of season eventual deals. Why not just stay with Tonje and Banton since I believe they can afford it? Shulga and Harper as 2-ways can still be available to the team. No need to do anything different until the last day of the season.
Am I missing something?