The $300 price point is pushing the limits of what I can recommend as a useful microscope.
Most of the microscopes in this range are toys, and do not have sub-stage condensers, which means that the high power objectives they come with are almost useless.
Here are some remarkable exceptions:
-
Wedmore SP03 Microscope $134 http://www.brunelmicroscopessecure.co.uk/acatalog/microscopes-monocular.html
-
Monocular Student $190 http://www.lowestpricemicroscopes.com/40x-1000x-magnification-monocular-student-compound-light-microscope/
-
Wedmore SP14 Microscope $215 http://www.brunelmicroscopessecure.co.uk/acatalog/microscopes-monocular.html
-
SP27 LED Microscope $216 http://www.brunelmicroscopessecure.co.uk/acatalog/microscopes-monocular.html
-
Konus Academy 1000x $235 http://www.microscopes.com/ms-ko-mi-5325.html
- Binocular Biology $276 http://www.lowestpricemicroscopes.com/40-1600x-compound-binocular-biology-microscope-plus-slide-sets/