I suggest making sure that this individual wants to participate in the first place. It may be a case of something they're really not interested in and may not have the extra funds to do so making them just feel resentful of the entire thing.
The first year I participated in Boyfriends families secret santa Boyfriend hadn't actually ASKED ME first before telling his mother I was participating. He just assumed that because he mentioned that's what his family does that I would be joining. I was unemployed with barely enough money to buy gifts for him and my parents and then to have another commitment placed on top of that? The gift's where set at $50, $50 I didn't have and would have rather spent getting my mother and father something if I was going to spend it in the first place.
Boyfriend pitched in half to help me pay for it because he felt awful for committing me to this when he found out how horrified I was that he'd done so. But it was still very stressful for me to shop for someone in his family I barely knew and struggling with money I didn't really have but had been committed to spending by someone else.
I am not saying that your co-worker is in a similar situation but that it's something to consider and could lead to them feeling resentful of the entire thing.
Oh and in case any one is wondering, Boyfriend and I had a talk about the difference in stating something and actually asking if someone is participating. He now understands that when he just mentioned his family tradition to me he wasn't actually asking me to
participate. Now he makes sure to clearly ASK things instead of stating them.
On the topic of getting things that amount to a total of $X event after discount:
This year for the family secret santa (that I agreed to participate in this time!) the price has been reduced to $30 to suit everyone's budget easier (if only it was last year..

). I drew Boyfriends sister and was told that she likes earrings of various sorts and so I went to a department store to begin my search. I found two different earrings both in a style I was told she liked: One is silver hoops with crystals embedded in the hoop, another are small dangly ones with round crystals and smaller silver ones encircling the larger round one. Both of which where on sale, if not discounted they would have come closer to the $40 range but together they came to just under $30.
It is my personal choice to purchase gifts that now amount to the $30 stated. If I am able to purchase something that is normally more expensive for an amount that is within this price range it just means that I am getting a great deal on it. But if I am still $10 short on the $30 cap I am going to see what other great deal I can find in that range and I managed to do so! Maybe I could have gotten a nice box of Christmas chocolates for the other $10, or a pair of winter slippers or something else not-jewelry related if I hadn't found the deals I had to purchase two sets. I personally view it to mean that your gift or gifts cost $30 to purchase, not that they value at $30 so I end up getting some great deals on a few things and pack them together.