I love that we jump directly to "deception" rather than "this could be a mistake"

A better approach would've been:

"Your website shows "Starting at 959 for the DIY option, but when I click on it the base option starts at 1,049. Am I missing something or is this a bug, an explanation would be welcome."

As the sibling comment noted, the DIY button was pointing to the pre-built configurations and vice versa. We're fixing this now.

Edit: This is fixed now.

It looks to me like the links for DIY and prebuilt are reversed.

you're mentioning euros and GBP as well though; could currency conversion and import taxes explain the difference?