Hi guys, I know that this was discussed before.. but I can not find those threads

I will soon need a suitable (and not too expensive, please) coma corrector when I get hold of Canon 400D.
Are there any other than Baader and are there any suggestions and recommendations that I should observe? My mirror is F5.6.
Where will be the focal point after installing coma corrector?
How it is supposed to be istalled (how far away from the sensor plane etc). I need to know this in order to design the adaptor for a camera....
Thanks in advance...