Weapons aren't balanced in terms of cost IMHO, it's knowing how much power your ship can put out and making sure to have a mix of laser for shield and projectile for hull, at a basic level. Cheap gimballed multi-cannons seem to be ideal for close in hull damage, while a good beam laser is great for taking down shields. As for the A-G classes, I find them unconnected with the quality, but the range of available weapons, especially the overcharged, focused etc. "special" weapons seem in short supply, so it's hard to create an accurate picture of where the classes and variety of weapons correspond to price and availability.
Also, came here to pass the time on a 70K LS trip exploring, just saying.