Over the years i have met various singers who had not one bit of musical ability or funds to gain studio time or knew musicians to work with or get ideas from.
Several of them fell prey to the what is known locally as the Music Mafia.
Small or home based studios promising a demo for a small fee but often taking thousands and giving little in return with badly recorded or self indulgent backing tracks. In many cases it's a Midi driven cover or worse a track off a Karioke CD.
Now there are some good studios out there who do offer a proper service so its not all bad.
But there is an alternative. Instead of paying for a lame demo post your vocals to a site like CC Mixter and if its good your vocal work will be turned into a variety of musical styles.
Admitted you are going have to produce your vocal in some way by recording it your self and singing it in tune and set too a least a click or metronome track at a marked tempo.
But the money you will have spent on a poor demo will be better directed to purchasing a good mic, learning some know how and recording it yourself.
You have nothing to loose. Your work will enter under the Creative Commons banner but you will have possibly have 10 well produced demos or more you can play to people and your own microphone or a small digital recorder at the end of it.
There are thousands of PC based musicicans who can't sing a note, desperate for vocal stems to work their magic on . So if you have a voice let it be heard and get it online.