As magnification increases, your main spend requirement is glass. Light is now cheap in the form of LEDs, as are condensers/collimators (which are not strictly required). IMHO at most magnifications you will get better relative image quality enhancement from adjustable through-light and correct focus than from a prospective upgrade to collimated light. Cheapest way in is a mono 'zoom tube' system which incorporates configurable magnification and ties directly to an industrial CCD camera. This is 'digital native' and obviates the need to pay for additional elements including a rigid stand, a stage, a revolving nose piece, and multiple high grade objectives. If you buy online, you can get a lot of value for cheap. However, you then need to fudge a stage, a light source, and a condenser, none of which are hard. These systems are super fun because you can route HDMI or USB to a big screen and share exploration with others. If you find microscopic critters, you can even record videos of them doing their thing. If you want more detail resolution, you can patiently twiddle or automate the focal adjustment then do focus stacked images. However, to get really good results you need to start getting in to things like chemical staining, frozen sample preparation before microtome sample slicing, oil-immersed objectives, and high quality glass, at which point you are really better off with a traditional microscope. Once you have the platform it's the glass that costs money.