While I await your answer I'll give some answers based on guesses:
Assuming there is a drawing of slips of paper with names on them. Assume the drawing is open for entries for a month and then closed.
From your "already determined" phrase I assume there are a number printed and made available. Let's say 100,000.
But not all will be used. Let's say 50,000 are filled out and turned in.
Assume the slips are drawn at totally randomly after being well mixed.
The odds of any one being drawn are now 1/50,000. It doesn't matter if it was put in first, in the middle or last so spacing makes no difference.
If you enter 100 out of the 50,000 your odds are now 100/50,000 instead of 1/50,000.
However, let's say each entry costs you $1. And the prize is $20,000. That means that before the draw each ticket is worth 20,000/50,000 or 40 cents. That means on average you will lose 60 cents each time you buy a ticket. If you buy 100 tickets you are most likely to lose 60 dollars instead of 60 cents.
That is all before the draw. At the moment of the draw 1 ticket becomes worth $20,000 and all others are zero. The average is still 40 cents each.
Before the draw you are buying 4 dimes for one dollar. If you think that is a good idea or can afford to make that deal once or 100 times then go for it. But be very clear: You are buying 4 dimes for one dollar!
It's not gambling per se that's a losing proposition, it's the payout system.
It could easily still be a gambling with a more than 100 % expected value to a "ticket".
Referring back to my example: let's say someone donates $40,000 additional to the pot - perhaps to encourage more tickets to be turned in. To keep the math simple let's say that didn't work and 50,000 tickets are still entered.
The payout is now $60,000 so the expected value of a ticket is now $1.20 which you buy for a dollar. By the raw statistics the ticket is now worth more than you pay and buying more makes sense. But most can't buy all $50,000 entries.
So if you buy 100 tickets for $100. Your statistical payout is $120. But only one ticket will win so the mostly occurrence is that you lose the entire $120 dollars. In fact, it's still almost guaranteed.