We have, for about 3 years, used a Medion system from Aldi, of all places, which cost approx £230 when purchased but I seem to remember seeing them down to £160 a couple of months ago!
She's never missed a beat, the only time she was "wrong" was when we were heading for Thornborough, Yorks we, in the middle of the night and totally reliant on the Sat Nav, came across a newly constructed by-pass which wasn't mapped and suddenly found the little pointer arrow in no mans land for 4 or 5 miles but as soon as we came off the by-pass she resumed on the existing road.
The system has cashpoints, police stations, cinemas, theatres, petrol stations, supermarkets etc etc mapped but there is no "speed camera" function which is no problem if you do not speed!
Not the most technically advanced system but does what it says on the tin!
My Twopenneth on the subject...