Birthdays on a Budget--Shark Attack 4 year old party

Looking to celebrate a young ones birthday on a budget.  We are trying minimalistic party options and wanting some FUN QUALITY time with our almost 4 year old, his friends and dear loved ones.

This is what we are doing this year:

We are going to a PARK! With FUN (free) toys!

We are really praying that the weather will be nice!

We are playing fun and silly games like toss across (borrowed), squirt guns (gift for kids to take home) and parachute games (bought/invested). 

Kids will celebrate with some fun shark cupcakes (homemade) and water.

Requested that no gifts be brought--since time with my little one will be WAY more memorable!

Afterwards, family will gather (because many wont come to the kid park thing!) for a potluck lunch where we will grill out.

This party was a little time-consuming to come up with FUN ideas and then take the cost out. We are hoping that the whole day will cost us less than $250--which includes a kid "Shark" theme party for 15 (with treats and take home squirt things and beach towels) and meat for a family gathering of 12 adults & 5 kids.

We KNOW little (big!?) man will LOVE the quality and social time for his party and that some crazy things that cost a lot (rental, tokens, bounce house, you name it) won't even be missed with all the action!

What are ways you save money on birthday parties?