Tony, I have used a Garmin 72 for 3 seasons and found it ideal.
With the bracket attached to the front of the sliding hatch I can see the screen well enough from the steering position on my 26. You can set up to 4 different readings to be displayed simultaneously. There are no worries if the hatch has to be closed, exposing the set to the elements, as it is waterproof. I replaced my larger 'inboard' (French) set which failed within 3 years. Get the deal that includes the power cable(12v cigarette lighter socket)and bracket. Should be under your budget of £140. But I would also recommend the data cable so you can use your computer to generate the waypoints with a proper keyboard. I use the GPSU programme for this. Bit tedious otherwise with just a rocker switch.
It will also link to your DSC radio ... only just got one myself so can't say how easy this is.
Good hunting! Chris.
Chris Turner