Step 2: The List of Requirements:
Don’t worry. This is one of the least expensive major science projects you’ll put together.
You’ll need:
I found a sunny yellow ball for my Sun.
1) Any ball roughly 8” (19mm) in diameter—a basic playground ball is likely to work, as will a standard soccer ball. FIFA size 5 works for the English-units model; the SI model is slightly smaller, so a youth-sized FIFA size 4 is appropriate—but don’t get bogged down in the details. Visually, when compared with the planet models, all of these ball sizes look the same. It’s most likely that you already own or can borrow a ball for this project; if you simply must buy a ball, you should be able to find one for under $10.
2)Â A set of eleven objects to represent each of the eight planets, our Moon, and two of the dwarf planets:
Mars or Venus
Pluto or Ceres
a)Â four pins (two pin heads represent Mars and Venus, two pin points represent Ceres and Pluto),
The Moon Is Made Of Green Candy
b) one tiny candy nonpareil (cake décor or “sprinkle”) for the Moon
Earth Gets Spicy
c) two peppercorns or allspice seeds for Earth and Venus
Having a Ball with Jupiter
d) one jacks-size ball (Jupiter)
This jellybean could be Uranus or Neptune
e) two jelly beans (or coffee beans) for Neptune and Uranus
Saturn represented by a large swirly peppermint
f) and a ¾” (19mm) “shooter” marble or a big round piece of candy (also 3/4″ or 19mm) for Saturn. (It’s just so nice to have something extra-cool and colorful for our most spectacular planet.)
Total cost: less than a dollar US; ideally, rummaging about an average home or allowing participants to bring contributions should turn up most of these objects for free. To splurge, pick up a whole jar of fresh peppercorns for around $5 and share them out among the students.
2) Eleven inexpensive holders for your objects, with the object names written on them. Empty clear yogurt containers or plastic drink cups work very well (see photos), as the pins can be pushed through the cups and others attached with glue to the cup bottoms…such that the cups then serve as mini-pedestals for the model objects. However, don’t feel bound by guidelines here—a set of index cards will do the job if that’s what you have handy. It does help to secure each object to its support. However, be sure that students can see the actual object clearly so that everyone has a feel for the scale. Cost: as much as 10 cents
3) A few signs printed on regular-sized paper to leave with objects that will be waiting for your return, such as: “Please Leave This Experiment Undisturbed — (Teacher’s Name).”  Cost: 10 cents
4) Weights to keep each sign from blowing away in a breeze—anything from a handy rock to a water bottle to an actual sports-field marker from your supply closet.  Cost: negligible
5) Your basic first-aid kit and/or other equipment required by local protocols for a field trip.
6) Water as needed (Up to $10 if you need to buy each student some bottled water; negligible if students can bring refillable water bottles.) You may choose to make the walk as short as a half-mile (kilometer) or as long as twice that. For a short walk, you should only need modest supplies; for a long walk, snacks and water will be welcome.
7) A printout of your “Cheat Sheet” for either the English-units or SI-units version of the project Walk to Pluto, Miles or Walk to Pluto, km  (Just click to download the desired document) Whichever measurement system you’re using, it’s just one sheet, front & back, and includes short comments you can make as you take your trek. Cost: 15 cents, if your printer ink is expensive, because it does have colors.
Total cost of essential supplies: normally about a dollar, assuming most items can be gathered at home or borrowed.  For bottled water, if needed, budget an additional 50 cents per student
If you purchase all new supplies, you could spend as much as $40 for a brand-new soccer ball, a jar of nonpareils, a jar of peppercorns, a packet of pins, a jacks game, a bag of marbles with a shooter, and a package of jellybeans.
Interested in more details about the project calculations? Here are copies of the complete worksheets: Walk to Pluto Databank, miles and Walk to Pluto Databank, km
(For workbook copies in Excel format, ready for editing, I can send you a copy via Facebook messaging. Just connect to one of my pages, Pixel Gravity or Cometary Tales. Say, while you’re there, “like” the page. Either way, you’ll receive the file in a return message. The beauty of this approach is that you don’t even need a copy of Excel to use the workbook—Facebook will prompt you to choose whether to open it in Office Online or to download it. The alternative is to email me via cometary@cometarytales.com.)