All of these used gauges will be far better than a new FO gauge and even a new Davis.
Might get this for a reasonable offer: (I assume you will not pay the huge postage offered on UK site)
http://www.ebay.co.uk/itm/Texas-Electron...1438.l2649
This one comes with pyranometer which with a bit fiddling you can probably get to work with Weatherduino.
http://www.ebay.co.uk/itm/Texas-Electron...1438.l2649
http://texaselectronics.com/products/rai...gauge.html
And an interesting one which you might be able to make your own enclosure
http://www.ebay.co.uk/itm/Sierra-Misco-I...1438.l2649
http://hydrolynx.com/manuals/5050P.pdf 1mm resolution but very accurate.
Might get this for a reasonable offer: (I assume you will not pay the huge postage offered on UK site)
http://www.ebay.co.uk/itm/Texas-Electron...1438.l2649
This one comes with pyranometer which with a bit fiddling you can probably get to work with Weatherduino.
http://www.ebay.co.uk/itm/Texas-Electron...1438.l2649
http://texaselectronics.com/products/rai...gauge.html
And an interesting one which you might be able to make your own enclosure
http://www.ebay.co.uk/itm/Sierra-Misco-I...1438.l2649
http://hydrolynx.com/manuals/5050P.pdf 1mm resolution but very accurate.