You don't have to buy him as a 'new player' this year. Buy him for what he was last year (2.9 WAR). Even at his shittiest, he was worth 1.5 WAR over a full season. The floor is pretty damn high here.
I think the point is Seager would be a cheap option in terms of he won't cost us much in the way of prospects. He's expensive, but given the payroll position we're in, who cares. I don't have a crystal ball, but he's been trending up since the start of the 2018 season. I think someone noted injuries hampered him in 2017 and the start of 2018.
https://www.fangraphs.com/players/kyle-seager/9785/graphs?statArr=61&legend=1,2&split=base&time=season&ymin=&ymax=&dStatArray=
Maikel Franco sucks. A.Cabrera would be another option for this year, but he's an impending FA. We need someone solid at 3rd now and probably until the middle of 2022...