If you don't mind playing this game again and again and trying to get a rank for every character in every chaper(that make 7 campaign in 4 different difficulties so 28) you will eventually have enough skill points to buy what you want.
I did the game on normal first with the characters. Now im taking the other one for an amateur run(doing emblems) and after that ill check if im ready for pro or i pass by veteran. Not sure if i will do the 28 chapters with ranks...lol but well... i think pro should not be a problem with all the skills in the game...
Gears of War Legend