There are a bunch of fill in the blank shopping cart setups and ways to add customization to signs without having a sign builder. I feel like those sign builders are a PITA and attract the cheap asses but I could be wrong. That is fine for a wholesaler but not ideal for a smaller operation. I will say that it is a lot of work to keep up with the site in terms of adding products, changing prices etc. It could easily be a full time job for someone. I have shied away from it lately, it's too much to keep up with and there is plenty of local business to keep a small place busy right now.
Once it's set up, you generally leave it.
Only time you need to update price is if the price of material changes or you've changed printers.
Depending on the complexity of your products too.
Say you sell simple products like posters and they're all set sizes only. A3, A2, A1, A0. and other similar products. You can just export the product data to a CSV file Change the prices and import it back in.
If you have a site like wordpress, you'll have more maintaining to do as plugins and themes have updates etc.
As for the "designers" or "sign builders" i think they're great.
1. your customers don't need to bother you to design their sign.
2. your customers what to add or change a phone number. they can easily do that.
3. your customers will probably never follow artwork guidelines, so having a cropbox that will show crop/bleed & safezones are helpfull.
4. everything that comes out from it will be a print ready PDF.