Hello. Want to fit some locks onto my original wooden sash windows throughout the house. Have been told the easiest and best way is to fit two restrictors either side of the bottom sash (to stop them being opened or closed). Is this the case? Had a quick look at my local locksmiths and have been told they'll cost £10 for a set of 2 per window. Seems a bit steep for a tiny bit equipment, especially as I have nearly 20 to fit! Any suggestions for other ways or where I can get them for cheaper? much appreciated. Cheers