There are cheaper dovetail plates, but I don't think they will fit over the top of the existing bar like the one I got, which is flat on the back and didn't need any modification to go with the rings. I could be wrong, so make sure to measure if you go into Bintel.
BTW, I'd love to be a fly on the wall as you "defiantly" get those rings.
(Sorry; couldn't help it).