help me.

i honestly feel that my even POSTING this query is moot (not to mention embarrassing, because i suspect i am the cause of this small misfortune...), but....before i head over to "the Hub" (which is Providence's sneering coterie of bike people, all things fixie, a distasteful eyebrow-raising establishment if you (or rather, i) ask them to special order a clangy, horrible bell for your bike---i DID do this though, and after some cocking of my head to one side and self depracating remarks, the lad behind the counter grinned, and two weeks later LO! clangy bell had arrived from parts unknown....but that isn't what this story is about....) and face jeers, appalled glances, or laughter....

my back tire all of a sudden has a curious bulge in it. gruesome. it's sticking out almost perpendicular to the tire/tyre. for the past 3 days, every time i have ridden my bike (which has been at night, in the dark dark), i've felt some strange drag...but then, yesterday, noticed this ghastly thing and have not ridden since, since i anticipate it exploding in a terrible way. i need new tires anyway, these are old and are flirting with being dry rotted, but....is this going to be a terribly costly affair? please help a lame, raleigh rider....