Been thinking about these solar panels too David.Laurie's post is about right,for that size unit.
Have a look on ebay,I did see a 120W one cheaper than the one in your link,but your one might be a better build.
An important part is the regulator,many say the ones they come with are ok,but down they track get a better one and attached for better input.
Anyhow here is an ebay one
http://www.ebay.com.au/itm/150765161...9#ht_554wt_952
I think getting one of these,or the one in your link is a good investment,I'd be interested to see how you go.Cheers C