The way you're putting it, it seems like any mouse would be an upgrade to your current one
You mentioned that you prefer a wireless mouse. I don't have any significant knowledge in that area but I do follow wired mice. An upside is there are many cheap ones around and somewhat more shapes and specs to choose from.
I'm currently using an old Microsoft Comfort 3000. The build is a bit sturdier compared to your sub $20 mouse. However, I much prefer a one handed design as opposed to an ambidextrous one. I've tried ergonomic mice with ring finger and pinky rests which are really comfy.
One I'm interested in is the Mionix NAOS because of its finger rests and the softouch coating - personally, the lighting is a bonus.
http://www.amazon.com/MIONIX-Multi-Color-Ergonomic-Laser-Gaming/dp/B00ANIRU7U
There are 3 models - mostly the same except for the sensors and the presence of the DPI indicator on the 8200.
Linus' unboxing/review: https://www.youtube.com/watch?v=qvlExWJmbGA
HardwareCanucks' review: https://www.youtube.com/watch?v=2BvxmLmV9TM
Of course there are many others and I hope this helps to expand your search for a new mouse!