I paid £3,500 for my first one back in 1997/8 it had to be fitted into the Van, it was an Alpine DVD based unit and did a good job it came with a TV aerial too, I had it in two more vans after that but figured out it was pretty basic they just said it was an impossible DIY job unless you were a autosparky, but it was basically a few plugs and a couple of cables for the power and earth, it sounds a lot but I was earning £1200 a week back then as it was still boom time after the big postal strike of 1971? this is when all the courier outfits started up to move mail about, they never got it all back, I had a Garmin que3600 after that, it was also a PDA and was better for the job, and then I started using a Laptop with a GPS antenna and Autoroute with GPS enabled, that was the best as I just put the postcodes in, click optimise and set off, best out of all of them, but some scrote nicked the van while I was delivering down in Wolverhampton, the company had CCTV, which showed my vans reg Clearly, and the van that the scrote got out of was sign written, I the manager rang them in less than 5 minutes, they did sweet FA and even refused to come and talk to me, didn't want the footage or anything, that cost me £12k as it was a fairly new rental as I had a contract to deliver and my van was in dock.
I still have the GPS antenna though and it still works.