I think we need to aim a little lower. A guy I have my eye on is Quinton Spain, a 28 year old left guard who fits a zone well. A Josh Kline type. Probably better actually. Played 4 years in Tennessee before moving to the Bills last season. Run blocking is up and down but he anchors well. His "pass-blocking grade has been 75.6 or higher all four years of his career." Which is a a huge upgrade over Elflein.
Besides that, Brandon isn't even a ZBS guy. Could he fit the scheme? Sure? But why overpay for a guy you would need to mold? Especially when we just saw the 9ers get it done with a journeyman RG, backup Center and former bust from another team on their interior? They win the damn game if they just hand it off like 4 more times in the 4th Quarter.
Upgrading from Below Replacement Level to League Average(ish). That's what happened with Remmers to Kline. Expect the same going from Elf to (Insert Tier 2/3 FA or early Draft Pick here).