The $29 plan is enough for most Etsy sellers to get started on Shopify.
The main benefits of the $79 plan are, the ability to sell gift cards, and the ability to recover abandoned carts using email autoresponders. The transaction fees are also slightly lower on this plan, but unless your sales volume is high, you won't benefit much from this.
If you already have another website (e.g. a Wordpress site or a blog), you can use the Shopify Buy Button to add your products to that website using the Shopify Lite plan for just $9 a month.