Not knowing what kind of equipment you have and also not knowing to what extent,quality and budget you request, I'll assume that you simply want to record a pre-recorded instrumental c/d with your lyrics layered on top economically.Why don't you check out a Tascam Porta 02 4track cassette mixer recorder. It will allow you to play your pre-recorded music and place vocals in your mix while
recording both. They sell for $150,and even cheaper used.
Do you own a mic? or other equipment? Have you thougt about recording to your pc?