I own over 100 800 numbers. The big name carriers want $5 a line per month plus 2 to 3 cents a minute. I use a couple of different carriers, one I like is opexld.com, it is 2 bucks a month for the first line and 50 cents for each additional, plus 2.7 cents a min. If you just need one number, it may not be worth using another carrier just run it through your current carrier.
I recommend a 800 number not a 888, 866, 877 etc. Sometimes a 800 is hard to get. I agree with the rest, a vanity number is a pain to dial unless it is a great number and your doing radio or billboard advertising.
