Unless you are technically minded, I would say it's probably far better to pay someone to build it - especially if you are serious about making money from the website, rather than just simply having a little dabble.
ALways pay a professional copy that can provide a professional image. Use the correct text, understand the market. Unfortunately, there are people who say they can do it but they cant and its false economy. Building a professional website requires experience and lets face it there are some dreadful ones out there- sorry but puts me off.
ALso professional photos a MUST. Around £500 half day. Business cards/stationery etc all need to follow the brand image. Copywriting is also advisable and legal jargon - T&Cs etc need to be correct.
Having a company that can set up numerous e-mail accounts and understand your system is essential and if they are local they can pop up and sort out any e-commence problems you may have.
I use http://bigcartel.com/examples works very well for me, you can customize the design, but really your photographs are everything when selling online, so it would be money better spent getting a pro to do your photographs IMO. But like Saffra says, it all totally depends what you're selling?
why won't you consider Microsoft Office365? It gives you a website, your email (25GB), your office web apps (word, powerpoint, excel) and IM for just £4 per month per user. This is all cloud based and Microsoft will host everything so you don't have to worry about buying servers etc...
I work for a Microsoft gold partner and we are launchign support services for this now and I think this would be ideal for a start up or for a professional.
Drop me a line on my work email if you would like some more info.