Shopify is an option, as is WooCommerce (which we build a lot of our eCommerce sites from). Unless you’re planning to become massive – turnover and product range, then Magento is almost always huge overkill. It’s great, in the right hands but in almost every case we’ve seen its way too much (and cost as such) for what most clients need.
It all depends entirely on what it is you want the site to do, is it a single product? Is it a range, and do you want/need a shopping cart type set up? Are you selling to businesses or Joe Punter? Are you needing to work out delivery costs dependant on buyers location, size/weight etc?
A small site with A ‘product’ and a Buy Now button linked up to PayPal could almost certainly be designed and put together in a day, at a fairly low cost. But.,, there’d be little point if it wasn’t what you or your buyers needed.
How many transactions are you expecting/hoping to turn over each month – thatll determine whether PayPal is your best bet of it it’s worth looking at something like Stripe or SagePay etc.
Ultimately, it can be as big or small as you like, but a wee bit more detail and I could certainly give you a decent steer.