Amazon have a couple of copies of the Somerset Wills book listed and the first one is being sold by Oxfam, so although it costs over £30 you could at least look on it as a charity donation:
https://www.amazon.co.uk/gp/offer-li...7&sr=8-1-fkmr0
Oh, or you can buy it from Somerset Record Society for £15 + P&P:
http://www.westcountrygenealogy.com/...ationslist.htm
I can't see how you buy from them but there are contact details on here:
http://www.westcountrygenealogy.com/.../somrecsoc.htm