Decent good 1quality band pass filters cost money - they can be seriously expensive compared to what consumer grade scanners/receivers cost.
An excellent alternative for sourcing band passfilters is to go onto eBay and type in "band pass filters" - search All Catorgories of eBay. You will come up with a list of literaly 100's of used/2nd hand band pass filters.
Ban Pass fitlers are normally described by way of given their centre frequency first, followed by their bandwidth more often than not in a +/- Mhz formatt (i.e. how many Mhz wide each side of the centre freq). The bandwidth will often given as a -3dB figure, meaning by how much the signal strnegth contained within the band pass will drop off at the edges of the pass band.
Keep in mind that once installed this type of filter will allow you to receive nothing else - except that range or bandwidth within the band pass. If you are also, or still wanting to receive freq's not only contained within the band pass but below the lower 800Mhz range and above the higher 800Mhz cell range (i.e. it is only those 2 sets or bandwidths that you seek to eliminate and nothing else), then it is not a band pass filter you want, but a couple of notch or band stop type filters. Notch or band stop filters will allow you to eliminate certain frequencies or frequency ranges contained within your overall listening bandwidth. You listen right across the 20Mhz - 1200Mhz bandwidth but wish to eliminate say 3 or 4 bandwidths contained within your overall listening range because there are strong transmissions centred on them that bleed across and interfere with everything else e.g. you wish to get rid of 341Mhz - 352Mhz as well as 512Mhz - 513Mhz as well as 800Mhz - 825Mhz and lastly 874Mhz - 883Mhz ..... or some similar combination of problimatic bandwidths - Notch or band stop filters are what you require for this latter problem, not band pass.
Keep in mind as well, that as said above, filters connected in-line in your coax run = received signal strength loss, and as you add freq's to eliminate your losses will quickly start to rise. -3dB may not be to bad, but add just one more band stop filter which also has -3dB loss and you are now right down on signal strength by 75%!
It can all pretty quickly add up to having to then invest in a preamp as well
