Agreed, in the original ME3 it usually takes me ~3-4 playthroughs to purchase and upgrade everything. I wouldn't say I mind it terribly as most of the purchases are upgrades I don't need, but the DLC weapons and armor are pretty expensive, so if you want to try everything you'll need a good deal of money.
If anything, it'd be nice if the shooting range on the Citadel gave you access to all the weapons so you could try them all there before purchasing them. I don't think I've used the shooting range since my first playthrough of the original game.
I do have two suggestions: go to the Citadel to purchase items instead of through the Normandy store interface, as the Normandy has a 10% markup, and wait to purchase anything until after you have both of the +5% Store Discount bonuses from the Intel Terminal. The 10% reduction in prices makes a big difference.
Additionally, any weapons and equipment you don't pick up on a mission will show up in-store, so you can avoid some costs by making sure to pick everything up.
