If I were to host a tournament, would I be able to charge DP to join if the prize were DP? For example, the entrance fee would be 200 DP and the prize for 1st - 4th place would be 400 DP(1st), 300 DP(2nd), 200 DP(3rd), and 100 DP(4th).
In order to host a tournament you'd need to purchase the Event item from the Central Shop. That alone cost 2000 Duel Point. Not mentioning any prizes would be deducted from your own Duel Points. Unless for rare cases where you can get someone to sponsor your event, only then you won't have to pay anything.