An aquarium air pump is the cheapest method i know to aerate water. For your experiment, I would just use miracle gro, use one teaspoon per gallon of water. I would say you can use straight water for a control. Lettuce will actually grow somewhat ok in just water. I would use aeration though, just to keep the water from getting stagnant. Good luck with your project.

You can also put the nutrient return pipe high above the reservoir surface so that it causes bubbles in the reservoir....bubbles entrain oxygen.

Does Miracle gro work for hydroponics? I'm comparing growth to soil plants, and I'm using unfertilized soil as a control.
For my plants, I'm using spider plants and measuring the growth by weight.

Miracle Grow is a soil fertilizer and not an hydro fertilizer.

The main difference between hydro and soil fertilizers is the nitrogen source. Ideally, only calcium and potassium nitrate are used in hydro, where soil fertilizer often uses urea and ammonium based nitrogen. The urea requires a soil orgainsm that does not exist in a hydro system to convert to a usable product. The ammonium nitrogen can cause root damage if too much is used. It seems to work OK with up to 15% of the nitrogen source. Ammonia nitrogen can be used in moderate amounts to bring a high PH down.

So where can I find a hydroponic fertilizer?

Try here:

Here is a link that might be useful: Nutrients

Well, the OP was concerned with the cost of a cheap air pump, I figured I would suggest MG as real hydro nutes are way expensive and he only doing a two week project anyway. IF an $8 walmart air pump is too much, then I think $25 or $30 (judging by the prices in the link provided by the last poster before mine) in nutes will surely blow the budget.

Kind of hard to conduct an experiment without the gear you'll need, such as a pH pen, and proper nutrients. Can the school provide anything?

As for aeration, Id use a hydro method that wont need an air source. You might look at rockwool cubes/slabs and you could also consider a vermiculite/perlite mix.

Dyna Grow nutrient is probably the cheapest you'll find. Try wormsway.com for that or if you have any local stores they may have a few sample sized packs they can sell you. goodluck.

For a sience fair project using spider plants. They will grow and root with just water.
I've seen school hydroponic projects that use blowing bubbles with a straw for airation. An aquarium bubbler isn't very $$ but there are some plants that can do ok without much airation spider plants, photos and even some lettuces included.
As for the nutrients, I've purchased 1.5 lb containers retail locally for less than $13.
Of course at school they may have pH test strips that could be used and perhaps the chemistry lab would even have many of the things needed to mix up a nutrient solution from scratch. Of course that would probably require a bit more research to learn what all is needed.