It runs Magento(!).
Ew, bloaty. It looks a nice, clean site though.
We did have a quote for a monthly retainer from the company who built it initially but it was too much to lay out each month. We'd still then have the issues of someone to do promotion on the site and email marketing on our other products. I'm the most technically minded here and I just don't have the time but we've spent good money developing the site for it to be sitting there. We do get organic sales but not many so really need to get onto it.
Salary wise I don't think you'd get much change from 20k, after all you'd need someone with web
and marketing skills. I guess you might get lucky and find someone straight from uni/college, someone wanting to start in web work who might do it for less, though they'd probably move on after a while.
Personally I'd approach a few smaller web companies or freelancers and get some quotes for the web updates. Regular update work is very attractive to smaller companies as it's a guaranteed income. Likewise with the marketing, I bet a lot of smaller companies would bite your hand off for this work.
You'd then have specialists working on each area, and as well as just taking on the tasks you provide them with, they might also make suggestions and offer other services to increase turnover that you hadn't though of.