The Regal seems to be the best of the cheapies, but if you can stretch to it a second-hand Dobro from the US offers better value. There are two or three places in London that usually have resonator guitars, especially Hobgoblin and Ivor Mairants - both in Rathbone Place. Music Ground in Doncaster used to have a few.There are some people in Leeds that make the best in the world, called Beltona, but they're very expensive (4k upwards)