Absolutely, I think you need to replace 4 linemen and right now.
The mentality that you can't replace 4 is based on nothing. The reality is that the line was an embarrassment last year. The reality is that we were ranked 31st in the league in rushing yards, and 27th in touchdowns. This isn't conducive to winning games.
We had 3 new starters in the secondary last year, and this year we'll have a 4th new starter with the replacement of sensabaugh.
We have options in the draft and stop gaps for the interim. The idea that signing a free agent to a 1, 2, or 3 year contract prevents us from being able to afford things in the future is ridiculous. You sign 1-2 free agent starters, and you draft 1-2 players to start in the first 4 rounds.
As I said, not doing so would be folly. You can get away with 3, but you should do 4. Two on the other hand, won't cut it.
Brandon Moore - RG
Jonathan Cooper - LG
Travis Frederick - C
Eric Winston - RT
Not only is that not overly expensive, but it's entirely feasible once you've addressed Free's contract in addition to Livings, Bernadeau, and Costa.