Tier pricing

Here is their tier table
0-10,000 transactions = $1,000
10,001-50,000 transactions = $5,000
50,001-150,000 transactions = $15,000
150,001-500,000 transactions = $30,000
500,001-1,000,000 transactions = $60,000

I would like to figure out a formula to where it will multiply users by transactions and it displays one of the tiers. That way I can adjust the number of transactions and it would change the to the correct tier pricing

For example: If there is 500 users who each make 1 transaction it would sum $1,000 or if there was 500 users who each make 21 transactions it would sum $5,000.