You & me both bubba. I've found that it's best for me to save up enough cash to cover one purchase out of 2 or 3 targets, so when I have near the funds I start looking. It seems to be working out that I can get the ship out of port and harpoon something every few months depending on the species I'm after.
This is a good approach I have tried it myself but constantly failed... I can´t stop searching, this is the problem, and I find something interesting much too often! Finally my empty bank account is the only way to keep me off buying