If we are going for a low cost upgrade that costs nothing of the future and leave room for rookies to grow and find their role in the roster, Bigras and Siemens come to mind, I am still going with Derek Morris and Dan Boyle as the two preferred targets on D.
Neither is a top tier player anymore, but the way I see it Boyle is a decent upgrade over Benoit and Morris is an upgrade over Guenin.
Hejda-Johnson
Holden-Barrie
Boyle-Morris
would be the D on paper, with Boyle and Hejda swapping around as game situations demanded. Guenin would ride shotgun as the 7th D man and you demoted Wilson to the AHL or trade him if there is any market for him at all. If you trade Wilson, an additional vet 7/8 D man would be signed.
Again, its not a massive upgrade, but it would be a much more stable blueline than any the Avs have had for 4-5 years. Both also add a massive amount of experience to the roster and improve the depth on both the PK and PP. It also gives you 3 units you can trust to play in virtually all 5 on 5 situations, meaning Hejda and Johnson both play less minutes during the regular season.
I figure Boyle will take a 3 year 4.5-5 contract to get him out of San Jose and Morris could be had on a 2 year 2.5-3 mill per deal. Both contracts would fit perfectly in terms of being deals that clear off as the Avs would need to sign younger players and neither breaks the bank. Both are also players you know you will get decent hockey out of. They do not have huge upside, but you know you are going to get a certain standard of play versus some of the higher upside guys that have more risk.