The reason your browser is telling you that is because their security certificate expired, and also because it was apparently purchased through their webhosting company (or a previous webhosting company, or just maybe they're reusing someone else's cert). As far as I can tell, they still offer the ability to use SSL, it's just that the certificate authorities use a business model of forcing companies to pay annual fees to keep renewing their certs. Neither of these necessarily means that their site is actually insecure.
If they're reusing someone else's certificate, that's a little more problematic, but I still don't think it's necessarily insecure. AFAIK the only reason to tie a cert to a particular web domain is to prove that you have connected to that site, rather than to someone intercepting your data. For a one-time purchase, the worst that could happen is that someone else knows you've bought a dog cock dildo and has your shipping address and credit card number. Embarrassing but you could claim it was a gift for a bridal shower or something.
If you are purchasing through them, you'll probably want to use a one-time credit card number (but that's true anywhere) or use Bitcoin if they take it. They might also use a third party credit card processor, in which case you'd be more concerned about whether that third party's checkout system security was good.
