Nowadays it’s not that difficult to build a low-cost ecommerce website. Depends on the money you want to spend and the look you want, you have multiple options.
If you only want a small ecommerce website and only have a handful items to sell with PayPal as the payment method you can use WordPress. It’s perfect for small businesses. There are plugins you can download to accept payments. However if you want to accept Credit Cards then WordPress is not the best way to go.
To build a more professional website accepting Credit Cards but still low cost, get a WordPress website and attach it with a Cart like GoDaddy’s EasyCart. Their cheapest plan is $9/Month and it is a professional shopping cart system. This is a great option because it is user friendly, easy to customize and cheap! Of course you will have to buy a SSL certificate to accept Credit Cards securely but that’s all. If you choose this option the cart would be built in under a sub-domain. For example your WP site is www.yourdomain.com your cart with Easy Cart by GoDaddy will be www.shop.yourdomain.com.
The other option to use Ecommerce websites like BigCommerce (I used them and they are pretty good and you might be able to negotiate on the setup fee). Well customizable, SEO friendly and user friendly. BigCommerce starts at $25/Mo.
I would not advise you to pick the cheap ecommerce sites that you can customize yourself in an hour. They usually wont work, they have bad SEO, very limited options, look ugly and so unprofessional. You would have to recreate your site in a few months because nobody will find it or use it for shopping!
The most expensive option is if you have specific needs. Then you will have to build your own ecommerce website from scratch. Of course this is the most expensive option and you will need a designer as well as a programmer.