Let's get a baseline with Shopify Plus.
While it is possible, to not build a custom site, this is probably the reason that you are considering this to begin with. Even if you go with a customized theme, you are looking at $20k minimum with reputable firm. You want a better experience for your customers, improves your reach, and grows your bottom line.
$24k+ per year
To use the Shopify platform, the fees start at $2,000 per month, and go higher after you pass $800k in sales.
Third Party Licensing
$500-1,500+ per month
Do you need any 3rd party provided utilities like subscriptions ($300+ plus sales %), search ($800+), or email marketing ($500+)? These costs are just an estimate, and could be more or less depending on your needs.
$2k-20k per year
The online world needs to be kept up-to-date, to avoid liability for security flaws. These would be on maintaining the code that isn't maintained by Shopify or any of the Apps you subscribe to. These costs will be significantly less than what you pay for the initial site build, but will be somewhat relative to that(i.e. a bigger, more complex site will require more maintenance).
2.4% + $0.30
While payment processing is some what a constant, it is certainly a cost (or tax) to be remembered. Deferred payments will also add costs here, as that convenience for your customers is a line item for you.
Shopify Plus Totals
1 Year Total
$52,000 - $268,000 + Processing Fees
The first year will be the most, due to initial development costs, assuming you build a custom site which Shopify Plus enables you do do. The Annual Expenses are included in this number.
3 Year Total
$128,000 - $344,000 + Processing Fees
It always is worthwhile to look what your outlay will be after three years. This includes the Annual Expenses as well. Also keep in mind, that especially after 3 years, you will probably want to make some both design and development changes -- and these figures don't inculde that.
These are the expenses you will pay each year to run the store, regardless of store revenue. They are largely composed of licensing costs, from Shopify and any other Apps from the Shopify marketplace.
Over three years you will be paying over $114,000 for Platform and App licence fees, and you will continue to pay that in perpetuity. The same fees over 10 years equals $380,000.00! While your numbers may vary based on what you need, if you understand why these number are what they are, we can help! And we can help in a big way.
Where would you rather spend $380,000?