No, it's not necessary to get Google Apps for business.
I personally recommend buying a domain independently from Google.
I've purchased a domain through Blogger once and it was a nightmare. (They assigned me a domain through enom at the time. The DNS setting I was given access to were incredibly limited and I had to jump through hoops when I wanted to move my domain away from Blogger. While it was enom, the settings page was like a Google re-branding of Enom and it was far from what Enom themselves offer.
I recommend going through Enom or Gandi or something and then pointing it to Blogger from there. I'd avoid the Google method simply for the lack of control Google gave me over the Enom account they'd assigned me. (This was in 2009, it could be different now.)
Setting up a CNAME in your DNS Zone is a cinch. Blogger will give you step-by-step instructions, depending on your registrar, to get you through it.