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Hi Mitch, welcome to IIS. You mention a cassegrain - you will need to decide what you want to photograph as this plays a significant role in choosing a suitable scope.
For example cassegrains are primarily suited to lunar and planetary targets, at high magnification. Their high focal ratios (typically f/10-f/15) mean they are not good for wide fields, deep-sky stuff (nebulae, galaxies and comets) - for these you need something with a much faster focal ratio, around f/5-f/7.
There are many here on IIS using APO refractors in the range 100-150mm aperture for this, for which they are ideal. Another excellent choice is a Maksutov-Newtonian - Orion and Skywatcher made a few cheap ones around 150-190mm aperture at f/4.5-5.6 depending on which model. And then there are the ones made by Intes Micro.
You can also use a fast Newtonian, anywhere from f/4 to f/6 with a field flattener and coma corrector; budget OTA's around 200-250mm aperture are easy to find.
Also do the maths on sensor size vs focal length, this dictates the field of view.
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