Don't laugh, but I started my route to actual singing via brett manning on a cd series.
Of course you can cruise through the cds, doing the exercises half-way, not putting much effort into them and call it done. Never repeat any exercise, think you've got it, and say it sucked. I've seen this happen.
I then ask the virtuoso what they got out of it, and they pretty much learned nothing.
When I did it I repeated exercises 5-10 times. Did them weeks, months later. The improvement was gradual.
I've also let friends borrow the set that have been singing since they came out of the womb and they have been amazed.
Are these as good as voice lessons? Likely not; but if you are interested i'm sure there are multiple cd series that are worth trying.