There are basically two types of H-alpha filters:
Wide bandwidth for deep-sky photographic use. These have bandwidths around the H-alpha wave length of about 2 Angstroms (2 x 10-10 metres) or more - usually a lot more. Typical ones are the Baader ones such as the 35 nanometer (35 x 10-9 m or 350 Angstrom) H-alpha Passfilter 2" for 125 Euro or the 7 nm (7 x 10-9 m or 70 A) H-alpha Schmalbandfilter 2" for 195 Euro. Or the 2 A for 485 Euro. These are only for deep sky photographic use - if you use them on the sun, even with something to block out most of the light to get it to a brightness that won't fry your eyeballs or CCD, alll you see is a deep red circle.
Have a look at:
http://www.baader-planetarium.de/zub...ter.htm#hapass
Then there are the narrowband filters - less than about 1 A, and to reslly see any detail you need about less than 0.6 A. The really good ones are down to about 0.3 A.
have a look at
http://www.baader-planetarium.de/zub...rotuberanz.htm
or
http://www.coronadofilters.com/
or
http://www.optcorp.com/ProductList.aspx?uid=471-306
As you can see, prices start at a few thousand and go up to 20,000 or so...
I have a Coronado PST which cost about $900 and I think it is barely adequate for only the most basic H-alpha solar observing. On a good day, and perhaps with a bit of imagination, you can see a few prominences and stuff.