$3 Million is plenty of room to give out a contract with clever contract structuring. And it doesn't really hurt a team long term.
For example: $50M/5 with $20M g $11M year 1, $20M year 2.
Year 1 - $10M bonus, $1M salary, $3M cap
Year 2 - $5M bonus, $4M salary, $11M cap (or even $7.25M)
Year 3 - $7 Million salary, $9M cap (or $10.25M)
Year 4 - $11 Million salary, $13M cap ($14.25M)
Year 5 - $12 Million salary, $14M cap ($15.25M)
That's backloaded as far as cap hits go, but it's pretty even as far as actual cash paid goes. And so long as Jackson makes it past the third year, the Redskins would be able to save a large amount of money if they needed to cut him. They'd even have the option of spreading his 2015 bonus out over the remaining three years, but that would come with higher cap numbers and equivalent cap hits for cutting bait.