Thank you for your suggestions,
Read their prior forum posts. That enables you to know that they're participating forum members and may reveal just how much of a beginner, or not, they are.
One problem though is: What if a beginner has been reading the forum for a year without having joined, or has joined and has never posted?
I don't want to cut them out.
You still need a way to choose a winning candidate, though. Although designing something is the first thing that comes to mind, I'm not sure what is reasonable to expect from a beginner (and how do you verify that they designed it).
Last time I just asked them to write up a post explaining why they needed this equipment, and used my Super Intellect
(that's a joke by the way) to discern whether they were being truthful. The problem with that is, if I allow brand new members to join just for this contest, and allow that, then a clever person could trick me into believing they needed the stuff when they just want it to sell on Ebay.
I could say, if you want to enter and have no posts, then you must have a history of 10 posts. But that allows anyone to join the forum, enter the contest, and try to trick the judge. If they are already joined before the contest I know their intentions are "pure".
Designing something even simple - I don't know how to ask such a thing without it being solved or found elsewhere and re-posted. It would have to be so simple the answer could be found by Google.
What about submitting what you'll be using the winning equipment for and then showing it being used as described within X days/months of receiving the prize. Choose the winner based on the use that fits some criteria that you establish (most interesting, unique, useful, etc.).
I could ask for photos of the proposed work area, or beginner project, but that cuts out people who can't post a photo. Maybe if you can't even post a photo you don't deserve to win.
I don't know of a fairer methodology still beyond asking for a short essay along with a picture of why they need this equipment.
As far as the contest judging, this time, since I'm supplying and shipping for free, would you like to be the one who judges the entries? Bet you didn't expect that zinger.