You can seriously make the same amount of money as made per hour in the video above me, by just getting 1st in deathmatches (which isn't hard at all). Just buy all the customizations for your best weapons, and start raking in the kills, I already have my face tattoo for 500 player headshots too.
Dude, you can't do deathmatch solo. Learn to read.
You sure can, solo (1 vs everyone else) deathmatches are very possible, and they are about 100x faster than doing any "solo" mission, since the payout isn't even determined by how many players are in the game. So why anyone would want to make money "solo" instead of a more efficient way makes no sense. And believe me, I'll never take the advice of someone who tells me to "learn to read" in a fragmented sentence.
Learn to read. It's an imperative sentence. "Learn" is the verb, and "to read" acts as the noun. Learn English.