Start with one genuinely free attraction
The Laguna Madre Nature Trail is the named stop in this lower-cost plan. The SouthPadreInfo free activities guide includes it among free things to do. That means no attraction admission; it doesn't make your transport, food or accommodation free.
Go during permitted access hours and enjoy the boardwalk at your own pace. It is a separate outing from the nearby paid Birding Center. Bring water and what you need for the weather so a short nature walk doesn't require an unplanned shopping stop.
Add beach time without guessing about charges
Compare city beach accesses for an entrance near where you're staying or already parked. Check the signs, the mapped spaces and any parking charge before leaving the car. County park entrances and city walkovers do not all have the same arrangements. A cheaper entrance isn't a saving if its walk or missing facilities won't work for your group.
Budget for the whole day
Add up the journey, parking, meals, drinks, rentals and any paid experience before comparing two plans. Use getting around and Island Metro for current transport information. If you're staying in a rental, check what its kitchen actually provides before buying groceries for meals you intend to cook.
Choose one paid activity if it matters to you, then get the total directly from that provider. Don't assume every tour price includes gear, transport, fees or gratuity. My Trip can keep the confirmation and your own spending notes beside this free outing.
Only the Nature Trail is added automatically below. Meals, a beach entrance and any paid activity remain your choices; the site won't turn a vague category into a booking or invent a price to make an itinerary look inexpensive.