I run a small business, but I'm already way worse off because everything I import costs a fuck-ton more and I can't afford to just bump prices up accordingly when my larger competitors already have huge warehouses of stock and have the power of scale to have negotiated pricing agreements. All the OMG RED TAPE that supposedly comes from Brussels is a myth, and what few anti-small-business legislation exists is hardly likely to be removed by the prevent government, whose ear is deaf to all but the largest enterprises.
Just as a counterpoint, as someone who also runs small businesses, but in my case tech-based ones that import very little but export information products and services, I have almost exactly the opposite experience.
The pound had been propped up for a long time and a lot of economists were saying it was overvalued long before Brexit was on the radar. Dropping it back to a more realistic level has already caused a big boost for our sales to customers over in continental Europe and beyond. It's dropped further than the necessary correction because of Brexit, but pinning the entire drop on that is unrealistic.
As for that EU red tape, it has been a significant burden on several occasions over the past few years, from consumer "protection" rules that don't really protect anyone but have substantial compliance costs through to the whole VAT mess where the EU seems to have done exactly the opposite of what it's supposed to do by making us suddenly have to deal with 28 different systems instead of one.
EU membership has its pros and cons, but in this specific area, it's very clearly not an advantage.