The Rev has spoken some wise word's here ,Gibblet is the man on our forum about string and cable's . I would suggest keeping your string and cable's waxed almost everytime you use it, or at least every other time . As Gibblet say's storage could be the factor why your string has broken ,if it's been away for a couple year's sitting and not being used much and also hasn't been waxed after being put away for a long period of time,then it's bound to dry out.
When your string start's to fizz up on you ,this is a sign of a string that need's wax ,the more you wax it the better shape your string will be ,it's best to wax often before frizzing appear's .As for changing your string ,if you have a proper press then it can be done without going to the shop ,but I would also suggest installing new cable's with your string ,it's just nice to have everything fresh and new ,nothing worse than installing a new string and then since your string broke possibly because of being in bad shape ,so most likely the cable will be in the same condition, so mchange them both and it will save alot of agrivation in the near future .
Ipromise you if you contact the Gib ,he'll give you a sweet deal on a complete set .As far as your peep you'll need to shootin [settle]the new string and cable's before you install your peep after 50 or 60 shot's should do the trick.
As for the cost you'll have to contact Gib on that ,but I'll say it won't hurt your bank account .Also your string and cable length should be written on a sticker that should be found on the inside of one of your limb's ,if it's not there then if you give John the make and model of your bow ,I'm sure he'll do a search to find it for you .

Good luck and remember to keep that string and cable waxed and you won't have to change it as often.

nubo