It is not cheap as a decent set of narrow band filters will set you back about $1200 dollars. Where it is 'cheap' is that you can use an F5 150mm diameter achro that costs $850 as compared with a $10k to $15k APO of the same aperture.
See this thread.
http://www.iceinspace.com.au/forum/s...ad.php?t=23971
There are others just do a search. Or ask.
Bert