You can get goto kits for EQ5 mounts but I think they are around $800 so if you could find a second hand HEQ5 you would be better to go that way mate.
Someone had a Meade LXD75 mount in Ice Trade ads for $700 if it's still available that would also be a good goto mount ... the #497 controller on them is excellent.
p.s. The other thing you will need if you are going to put your Dob on an equatorial mount is tube rings and a dovetail.