Here's a tip I learned from someone's dust video I watched a long time ago:

You have a bunch of slots for suit configuration. Take the time to set up multiple levels of suits, (STD w/ STD Weapon, STD w/ ADV Weapon, ADV w/ ADV Weapon, ADV w/ Proto Weapon, ETC). Once you've done this, click 'restock', and append the cost to the name of the suit.

That does two things. First, it reminds you of your suit cost, which is a great way to prevent lots of ISK in losses, as you're constantly being reminded how much you're spending.

Second, it gives you the ability to attack at a level that you're comfortable with. Losing alot? Go with a STD fit! They tend to cost 20k at most! Is it an even match, but you aren't willing to go all out? You've got an ADV suit for that! Remember - The guns are doing all the work; suits are where most of the cost comes from, so just fit a higher tier weapon than your suit, and build the suit around the weapon. I've started saving hundreds of thousands of ISK since I kitted out an ADV suit with a Proto weapon.

Since I started doing this, I find that I run ADV and STD a lot more than I used to, and I'm very much in the positive. I can afford to throw away a proto suit now and again. And truth be told, my STD and ADV suits are usually pretty effective when compared to the proto suits. Try it out, you'd be supprised :). DUST is not and does not have to be cut and dry Proto or MLT. There are other tiers in there :P

Edit: I will say, to fit higher weaponry and fittings with lower suits, you'll need to get those core skills way up. Just a heads up. They ARE WORTH IT!