A union wouldn't help. The P5 and G5 combined are 130 teams strong. If we rank programs on popularity and revenue, Iowa is probably an exemplar median P5 program, sitting pretty close to the middle. Most P5 schools below Iowa do not have any excess revenue with which to pay players. None of the G5 schools have excess revenue with which to pay players. So you would have about 100 programs out in the cold on this stuff.
The problem is if you pay the football team you have to pay the women's teams as well. There are only two conferences with significant juice on media rights and decent prospects going forward, the SEC and Big Ten. And even the Big Ten has a bunch of shitbag teams like Illinois, Northwestern, Indiana, Rutgers and Maryland who can't generate any appreciable amount of revenue from football tickets because they suck or don't have any fans. So if you have a union and they want $20k a kid, maybe Iowa can stretch and get it and cover the women's teams, but those listed programs above and places like KState or Iowa State would be totally fucked because they couldn't pay it over an appreciable period of time.
The huge schools, like Ohio, Georgia, Michigan, Florida, Texas, etc. would have no problem coming up with the funds. But once you get past the top 15-ish the situation would get shaky and once you got past the top 30-ish, it would be downright untenable.
The reality of the situation is that if you could jettison Title IX and then siphon off the Title IX subsidy there would be plenty of money to pay football and basketball players, but the bill trying to accomplish would be dead before it hit the floor of Congress.
Note that my inclusion of ISU isn't to bash them or you, it's the opposite. I want them to have a viable program, but with the changing conference landscape I seriously think they would be totally hosed if they had to stroke another few million bucks of checks annually to fund player salaries. And Iowa would be in the same boat if Ohio, Michigan and UPennState moved to the SEC.