The scope I use for guiding my C8 is a Sky-Watcher ST80. This is a short tube achromatic refractor that is lightweight, and relatively cheap. It won’t win any award for sheer image quality, but that does’t matter if it’s being used as a guidescope. It is also no slouch as a grab-and-go scope for visual use if you can put up with a bit (ok a fair bit!) of colour fringing.
These scopes are a basic, and widely rebadged, Chinese achromat. Similar scopes are made by Orion, Konus and many others. They make a great starter scope, and can be used later, coupled with a guidecam, as a guidescope. When you become more advanced and maybe want to try some imaging with a guidable mount, it definitely won’t go to waste..!