With today's RFA signings, the Kings now have close to $9M in cap space left. If they lock up Adrian Kempe to a long term deal (three or more years), I figure he'll cost somewhere in the $3 million range. Cal Petersen probably spends most of the season in Ontario next year and will be a regular with the Kings by the 2020-21 season, so he should get some term on his contract as well.
Next summer the Kings will have a slew of free agents and will have over $25M in cap space. Toffoli, Clifford, Lewis, Forbort, LaDue, Campbell, Ryan and Mario Kempe will all be UFAs. Grundstrom, Wagner, Walker and MacDermid will be RFAs.