This chart from The Guardian (and an article about it by Deadspin) are worth checking out if you have some time. It's a little wonky for us because it uses a 4-3 defense as a base but it's definitely still worth a read through.
http://deadspin.com/cool-charts-nfl-team-salaries-by-position-1265695011
http://www.theguardian.com/sport/interactive/2013/nfl-salaries-positions-2013-2014#san-francisco-49ers,san-francisco-49ers