You can sign ANY of the OTs on FA with a $5M cap impact multi-year contract.
The only possible exception being Whitworth.
The most reasonable candidate is 27 year old Wagner.
Here is a cap impact estimate for a 5-year $8M AAV (Wagner valued at $7.6M AAV) could look like with a $15M signing bonus:
-----------------2017-------2018------2019------2020-----2021
base-----------$1M---------$1M-------$1M------$6.25M--$6.25M
signing--------$3M---------$3M-------$3M------$3M-------$3M
restruct yr 2-----------------$1.3M----$1.3M---$1.3M----$1.3M
restruct yr 3------------------------------$1.75M-$1.75M--$1.75M
total:------------$4M--------$5.3M------$7.05M-$12.3M-$12.3M
2017 $4M cap impact is $1M less than Free's salary.
2018/2019 cap impact is less than Free's 2017 cap impact of $7.5M.
Before you complain about 2020/2021 cap impact, you could easily release him after year 3.
Then you have dead money of $6M per year for last 2 years - remember the $10M cap rise per year and the $130M open cap currently for 2020. Also year 1 and 2 of Dak's extension would be very cheap for a franchise QB.
Free rated as #3 worst in sacks and pressures.
That include LTs who typically get the top DE.