I found this application note from intersil describing simple autoranging DVM. The basic concept of this could be used in my Progmeter. 

Now I'm going to take better look into the AN and possibly test the divider on breadboard. I'll settle with DC voltage and resistance measurement for now - progmeter is not going to be replacement of DMM - even crappy 20USD DMM will be probably more useful than Progmeter, when it comes to DMM functions; but the power of Progmeter is hidden in calculator capabilities together with DMM functions.