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Let me start by saying that if optical quality is not key (and it sounds like it isn't), you can get a cheap 6mm Plossl new for $35-40 plus shipping. However, and please hear me out on this...
I think you will find 8mm to be a practical limit on focal length for an f/12.5 scope, especially with the central obstruction you will have in your mak. The laws of physics just aren't going to give you a special case. A 6mm eyepiece isn't very useful for most applications in a scope of greater than f/8 or so, no matter how much we may want it to be. My 6mm Vixen LV is "muddy" to look through on most scopes due to over magnification, and therefore until recently collected dust and only got used for collimation and the occasional double stars. A waste of money, really, when I could just use a 12mm with barlow for the same role. Now, the 6mm does perform well in my f/7 refractor, due to the lower resulting magnification. It is like sitting too close to the TV screen, the image breaks down around f/10 and only get blurry and dimmer as the focal ratio climbs.
Question: what is your actual budget, and what is the intended viewing target? Those two things would help dramatically in people's ability to make eyepiece suggestions. Also, I suspect that there are plenty of people in the Gosford area that could give you a look through a 6mm vs an 8mm and show you what that extra 2mm does to the image.
Eric
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