Or Star-mate...
www.star-mate.com/lx200.hm
But unfortunately I am no longer making them, as there was no real money in it for the effort. Shoestring will work fine.
I'd avoid the barlow if possible. What focal length is your imaging scope, and what is your imaging camera?
With your 70x500 guidescope you should get pretty good results upto about 2000mm imaging focal length. Some would say otherwise, but in my experience 4:1 ratio works ok.
Cheers