Don't do it Orestis.
Hang on to that $100 and keep saving, Christmas is only around the corner and trust me, it'll be worth the wait.
There were some concerns I had about this ep working with your "fast" dob. so I did a bit of research. From what i've summised, it works fine on slow scopes. On fast scopes, it seems to suffer the usual edge performance and astigmatism. If that doesn't bother you?
They talk about here on cloudy nights...
http://www.cloudynights.com/ubbthrea...1/Main/2267158
The 15mm is a good all rounder, it'll probably end up being your most used focal length, so please try to make this purchase a good one if you can - you have amazing observing skills and would hate to see you frustrated with an eye piece.
The Explore Scientific range seem to be a popular choice, many are happy with their performance, and their affordable.
http://explorescientific.com/eyepieces/
Have a look at a thread I did regarding choosing a 15mm ep- some great information is supplied on this thread, including much input from Mr John Bambury and other experienced visual observers.
http://www.iceinspace.com.au/forum/s...ad.php?t=71653
You can get a top performing Vixen LVW (65 deg. fov) around $220 second hand. Or even go for a Baader Hyperion (LVW knock off) new for $209 from OzScopes.
http://www.ozscopes.com.au/baader-pl...eyepieces.html
Note: You have a fast scope, cheaper eye pieces will tend to show up problems at f/5 and under.
As an example, with my 6" f/7 my 15mm Orion Expanse worked beautifully. On my 10" f/5 it's toast.
Astigmatism (sea gulling) so bad across the entire fov, I cannot even tolerate it. What you can put up with or how critical you are, I guess is up to you.
