I would focus ship purchases towards making more money until you've got a balance that gives you freedom to purchase whatever you'd like without concern.
Heres some advice i gave on another thread:
"I've recently started playing and i built up money pretty quickly by just trading jumping between two systems, one with a refinery economy, the other a high tech economy. Taking silver in the one direction, then performance enhancers in the other is a quick way to get onto a rapid growth curve. Do a few runs until you can afford a bigger ship (and still have money left for a full silver load), upgrade to a bigger ship, repeat. I used hauler -> type6 -> type7 -> type9. By type-9 you can carry about 650-700 and make about 20million per loop. With systems one jump apart and stations reasonably close to the primary star, its about 5 mins per iteration and with a landing and supercruise assist module its pretty effortless"