We started with prefolds and covers when DD2 was a week old (we would've done it from birth, but I had to order newborn vs. infant diapers). We did it until she was 3 mos. old and had a really bad yeast infection that didn't go away until we put her in 7th Generation diapers. We were using a diaper service so we think she developed an allergy to the diaper service detergent.
We thought about starting cloth using Green Mountain prefolds or fitteds w/covers again at 6 mos. old, but honestly we had gotten too used to disposables (and by that time had spent less on them than I did when we had diaper service) so I honestly think it's best to start with cloth prefolds very early on to get used to it vs. putting it off for 3 to 6 months because if you do that you are never going to do it. That happened to me with DD1 I was going to start diaper service (in 2006 unless you were really in the know cloth diapering was really still very underground and I thought the only way to do it was to use a diaper service :.....didn't visit this forum when I was pregnant!), but had zero time off work to nest before having DD1 so it never got started.
Also Gerber still makes the plastic pants so those are very economical too. My mom cloth diapered three children in them with no problems. Sure the snaps and the prints are really cute, but the basics still work.