Hetzers gonna Hetz, baby! 8)
If you're wanting to go really low-tier, I'd go for Bulldogs and Vedettes as the core of your armored force. Dirt cheap, respectable firepower, and just enough armor that they don't fold in half on the first hit. You need good tactics to keep them alive, but if you treat them right they'll never let you down.
To back these guys up and make sure they actually survive against modern opponents, you need force multipliers(read: dirty tricks). Conventional fighters are a wonderful way to give yourself some air support without springing for expensive ASFs, and they can pack a surprising punch. Nobody likes an AC/20 to the back, and nothing stops an incoming tank column like a high-altitude bombing run that literally covers half a mapsheet in mines. Remote Sensors are really old tech, but they can help you keep tabs on an enemy's advance strategically, as well as assist in indirect fire tactically. Plenty of civilian-grade vehicles mount extra comm gear, and the command bonus that can impart will be a huge boost to your faster units. Take a page from wars past, and give some of your infantry field guns. Infantry ambushes are bad enough, but when those infantry have a large autocannon hidden in that stand of trees or in that alley, things go from bad to infinitely worse.