You might contact the Florida cacher ocklawahaboy for info on how he made his coins. He produced trackable coins for his event. No unique icon, I expect to hold down costs.
A small budget won't produce a Geocaching.com trackable coin through a mint, with or without a unique icon. Especially not in those numbers. There are set costs, die fees, attached to a coin, and then "per coin" pricing, which drops with numbers.
75 to 100 cachers will attend an event in a State park, if a some number of caches are placed. If the budget is limited, spend it on quality containers. Just a suggestion. This will continue to attract over time, the event and coins will be a one shot deal.
You make a great point. The goal of the park is to increase visitors and they see the value in a new (or really not so new) user group who also shares a love for the outdoors via caching. Thanks.