I think $100 is very possible, but there is a lot of competition so you will have to work hard at it.
Well, lead sites (like azlyrics.com) get 5 digit profit monthly easily. If you have existing network of related sites (music/celebrities/video will work) you can get low xxx - middle xxxx monthly depends on size of the your network, your SEO skills and chosen conversion solutions. if you do not own other sites, where you can put links to the your new lyrics site - you will need to spend A LOT of time on SEO, because competition is pretty high in lyrics area. If you are not going to buy links, it would be near to impossible to get $100 monthly just from "free" SEO. BTW, its pretty easy to use lyrics sites just for the link selling. They have a lot of pages, if you will do some linkexchange and SEO you will be able to get PR 4-5 within a year easily, after that you should be able to get $100 monthly just from link selling.