There are many day trips from Prague, some of them are close enough to the city to travel there yourself and with the rest you are better joining a tour company – unless you hire a car which is my preference and they are quite reasonable. You will have to have a credit card to hire a car.
The Park is near Prague, it will take less than one hour to get there using the local transport system. It is possible to walk all day here and eat in the local restaurants.
There is an entrance fee of about 30 Czceh Crowns, less than one pound. There are loads of photos on the Pruhonice Park page.