Ghillie suits are under-rated, and a smartgun with redundant process manufacturing II will see through any ImpInvis spell running with less than 5 hits automatically. On an Ares Predator that isn't that expensive for professional opposition.
Thermal smoke also levels the playing field, and since mages can't cast most spells without line of sight it screws them over extra good. Flare grenades and strategically placed flash packs are also often overlooked.
To see through improved invisibility on a budget there are many options. one of the best is splash grenades with glow in the dark paint mixed with micro-tags. If they're facing it when it goes off they get a face full of paint and are effectively blind, if not then they're easily spotted because A) they glow in the dark and B) they have AR bullseyes painted on them and their location is showing up on your GPS. Good luck hiding that lot, chummer!
Of course, there are spells that can get rid of the paint and a tag eraser can kill the tags easily enough, but that takes time that you don't have in a firefight. (The spells are Fashion to get it out of clothing and Makeover to clean hair and faces). Don't forget that high end armour tends to have nasty object resistance to overcome for the fashion spell

Paint bombs work even better when mixed with neurostun and upsized to mortar or artillery rounds, if available...
Other cheap but cheerful methods of dealing with invisibility include tag rounds used in suppression fire, a hacker locating their hidden network and lighting it up (after all unless they have a mind-net going they're unable to see each other for hand signals or to even follow each other, meaning they either need to talk or have their commlinks on...), and other nefarious tricks of that nature.