Kris if you want something reasonable on a budget that will suit an f/6 newtonian like yours, stick to Plossls. Plenty to choose from, but the field of view is inevitably modest. The SWA and GSO ones under $100... they are OK in a scope at f/10 or longer - but not good at f/6.
To do significantly better than plossls requires something with green letters on it and that will cost well into 3 digits even secondhand.
See for example
http://www.iceinspace.com.au/forum/s...d.php?t=171209
http://www.iceinspace.com.au/forum/s...d.php?t=170845
Also see
www.astromart.com
To be honest theres not a lot wrong with an f/6 dob with a good mirror and a box of Plossls.