Basically just need to know the speakers, what frequency you want the rolloff to be, and how sharp it needs to roll off. A budget is also useful as all a HPF really is is a capacitor in series with the signal or an inductor in parallel with the speaker input, and caps of this size can range from cents to over 30 dollars each with the same being true for inductors. The way it works is that at high frequencies, a capacitor turns into a short circuit while at low frequencies it's open, and an inductor is a short at low frequencies and open at high ones. That means that at high frequencies, the cap allows the signal to pass and at high frequencies the inductor isn't shorting the signal to ground, thus allowing it to reach the speaker. The effect is the same: highs to the speaker, lows don't get through. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
PM me if you're interested, or I could probably teach you how to do it since it's really not that hard if you like learning about electronics and filtering //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif
edit: open means open circuit, aka, nothing gets through