The $500 connection fee is "the carrot and stick approach" to get you to connect. You think; $500 for a side sewer permit to connect isn't so bad, that is, until the HIDDEN additional cost of connecting that you weren't planning for show up .  Unfortunately, if you already paid your $500 side sewer permit fee and change your mind because you can't afford the connection, you can kiss that $500 goodbye, it's non-refundable. 

Do your homework, find out what it will ACTUALLY cost you before you pay your $500.  Ask someone who is planning on connecting what it cost them.  If you have deep pockets, it's your money.  If you are low income or on a fixed income, this sewer could spell financial disaster for you.  

Remember, once connected, your monthly fee will continue to increase at the county's whim. That $70 fee is 4 years ahead of schedule, if you think that more connections will reduce the monthly fee, it won't. The "estimated" monthly fee will hit $109.00 or more.   Can you afford it?