I've been looking to get a new Gro clock for 2nd child, looking around i found the usual sale prices of 19.99 for most of the bigger retailers, but here's the best deals I found.
The linked deal is for 14.99 with free delivery on orders over 29.99 (so depends on what else you are after, of if you have friends that also want one)
Other best prices i found were: £15 , but currently out of stock http://www.cuskishop.co.uk/gro-clock-sale-item-41-p.asp
or £18.99 with free delivery on everything!! http://www.powo.co.uk/index.php?route=product/search&search=gro%20clock
Hope this helps you.
This clock has been a sleep saver for us :-)