Giving money bonus on kill for one unit encourages a player to have a single money-farming gigachad.
Some ideas:
Hat gives +5 coins next round and disappears - that would make it medium risk medium reward item
First 3 rerolls are free - more predictable RNG
Make poison instakill after 3 seconds instead of gradual slow damage - counter to solo oriented teams
Make 3 separate slots for locked items - locked items are placed there and then bought/replaced. That would allow for better planning.