I have a small store. It is a small hobby but it makes money.
You see your question is not easy to answer. It can be 10s or 100s thousands of pounds.
It depends on your products, the number of your products and keyphrases you will be competing with others.
Also, it depends how much you are willing to do: on-page - keyphrase research, meta titles, headers, descriptions, alt text images, ulr optimizations; off-page link building, social media, Magento/server optimization, site speed load, PWA and such.
I personally did keyword research for myself using www.keywordtool.io and then approached a company called www.copify.co.uk to write products, page description. I only provided them with keyphrases I want them to use within the text. From what I remember they charge only 4p per word. I can highly recommend the company. They deliver high quality, unique not scrapped content withing 24-48h.
URLs, meta title alt image text also did by myself.
With regards to the linkbuilding, we used a company called linkology. They boosted out traffic pretty quickly for certain not very competitive keywords but we quickly run out of cash and not we aren’t growing anymore. They wrote for us quality articles and published them on high DA pages using guest blog posts technique. This should be still OK. They don’t use website built only for manipulating google signal. They are not cheap. I mean they were expensive from my wallet
Guys, please give us tips on how and who builds links for your stores. I know that this can be extremely expensive.
I hope that it is useful. It is worth to try copify.