Decker is the prototypical LT prospect NFL looks for, highly likely he goes first or early second assuming health and he doesn't completely blow up.
It is awfully hard to get drafted high as a pure guard prospect, so i'd expect Price and Eflien going anywhere from late 2nd to 5th/6th if they declare. Obviously a big range, a lot depends on how they perform this year. Also, I think Price has higher upside than Eflien based on measurables (he'll dominate the bench press at the combine).
Boren unfortunately will probably not get drafted. Just flat out too undersized for the NFL. As for Farris, he will likely go late/undrafted if he starts all year. It's hard to see him being substantially better than Baldwin and Baldwin wasn't in the draftable conversation.