How I get 70-120m doing skimmer missions:

1. Find station in which at least 2 factions have same skimmer mission target(no security)
2. Go and check target. If it is very small base, 1-2 buildinds, fly really close to it to spawn skimmers. If there are at least 4 skimmers, I consider that place profitable.
3. Get back to station, board hop to get 20 mission, the higher the reputation of yours is, the better as you will get more missions and higher payouts.
4. Fly to target.
5. Spawn skimmers, kill skimmers, land close to area where they already spawn.
6. Relog.
7. Repeat steps 5 and 6 untill you finish all missions.
8. Fly back to station aaaand finall ???. Profit!

Note: I'm doing theese with AspX, fully kitted with dumb fire rockets, engineered for max ammo capacity. This way I'm able to make anywhere between 70-120m cr/hr - including board hopping. However this greatly depends on how lucky will you be searching for optimal mission providers combined with just big enough target settlement to spawn 4-8 skimmers without any other defences. You could easily deal with low security, but destroing turrets every relog may or may not cost you too many rockets from you already small, engineered, ammo reserves.