Whoa nelly, hold yer horses!
Most of my credits have come from (npc) piracy, and in short order to boot.
For a low end pirate ship, hop in a Viper Mk.IV, it's got the internals for cargo, hatch breakers, and collectors, plus some speed and some tanky-ness. A cobra Mk.IV is a tad better for the job if you can get used to her sluggishness. The "Slow-bra" will net you about 32 tons of loot (at 51,000cr/ton or 1.6 million) per full haul. If you're good, you can get that in 15-20 minutes.
Not the "best" money maker, but definitely the most enjoyable in my books.
An Asp X, is basically like a bigger (64t of cargo) faster version of the cobra Mk.IV, batten down the hatches and hold onto yer boot straps! Profit ho!
From there, you "could" get into a python, I guess. But now you're just getting rediculous! Best to steal some poor saps orca, that's what I'd do. It's fast. Like awesomely fast, for a pirate ship. The one I've got holds 96 tons of goodies, plus all the fixins and tools you'll need. Engineer it and it's amazing! You'll be bathing in credits once you've got the skills mastered.
Just remember, choose your targets wisely. Keel back and up is where the money is at, so long as they've got mining lasers on board. Just be wary of mining pythons and T9s. They can be pirate-bane unless you're a really good fighter. (Seriously, you're in a ship setup for smash and grab against soft targets, if yer gonna fight, be prepared to limp home. )