I'm about to buy the 150pds which come with the same 6x30, I actually just found your post because I was looking for the same. After some research I can't find many cheap options, the cheapest I think it wold be the Astro Essentials 32mm f/4 Mini Guide Scope at 55£ and shouldn't need adapters as the focus range is quite large, come already with a skywatcher mounting, but it's 128mm FL and small diameter. Next best option, if weight it's not a problem, it might be a Startravel 80 but you need to find the way to attach it and just the ota costs about 90£, the Sky-Watcher EvoGuide 50ED Guidescope it's very nice, and expensive, 200£. But as I said, I'm not an expert, I just happen to be searching for the same thing for a few days now.