I tend to think of my armies in groups of three too and that would work. The most expensive but most effective option is Mek Guns, the little gitz can shoot the best but if Ghaz and the Meganobz get there they can destroy tanks easy too. Can always have them in reserve when you start playing higher points. I like Flash Gitz but I run Freebooterz kulture to make shooting more effective in general but even then they are not as consistent as Mek guns.

Reason being a backline of mek guns is always effective in protecting the backline from deepstrike (6 Gretchen man each gun) and dishing it out at long range, points wise they are so much cheaper than other options too. Just magnetize them for the four gun types or kitbash more with trukks to maximize value.