Why can't you set it up on facebook? Is there a specific reason why you need a domain name and a custom designed site.
If you're selling items and collecting payment over the net, you can use
www.shopify.com The only costs involved would be in getting your CC processor and/or Paypal integration up and running.
http://www.shopify.com/payment-gateways/singapore
Web designers are starving to death nowadays because it is so easy to get a website going that anyone can do it. I should know I used to be one.
If your website traffic is low, you can probably get by with a USD9.95 per month hosting package.
If traffic is high and you need a dedicated server, costs start at around USD100 per month.