I use metal boards with moveable magnets to teach many of the mathematical components of the grade 11 chemistry course. The cost to produce the boards and the work involved with making them is minimal when compared to the fantastic gains made by my students.
The metal boards can be obtained from many sources: scrap metal yards, metal super markets, Re-stores (operated by Habitat for Humanity), or thrift stores. I was fortunate to obtain my boards by recycling old metal shelves in my classroom, which were originally used to organize papers in a cupboard. Whatever your source, be sure to check that the edges of the metal boards are not sharp.
I use magnet sheets which I obtained easily from dollar stores. I sliced the sheets into squares approximately 2 cm by 2 cm. Different colour magnets represent different components such as units, constants, formulae, etc. White squares and erasable markers (e.g., overhead markers) are used to write actual numbered data. Number and letter magnets (the kind often seen used by preschoolers) can also be used. While such magnets may be obtained at education-type stores, be careful because these are generally pricier! I highly recommend thrift stores and garage sales to purchase such items.
Students become engaged when using the boards to build and manipulate different formulae (e.g., gas laws). When using the board to manipulate formulae, students can physically move different components around in order to isolate an unknown. The boards are also extremely useful when teaching the mole using the "ratio" method. Since the units are already made, the magnet boards allow students to use units easily and consistently. Units cannot be forgotten during the equation manipulation. Such a practice helps to encourage the students to use units as a double check. I make up special headings for my magnet boards (e.g., Given, Required, Solution) to help students organize their work in an efficient manner. A checklist can also be added to the boards (e.g., Significant Figures, Units, Therefore, etc.).
It is my experience that over the course of a unit — such as gas laws — the students gradually wean themselves off the magnet boards and begin to work through problems in the traditional manner of pencil to paper. I'm proud to say the original idea to use magnet boards to manipulate mathematical and scientific data comes from my mentor, Steve Quanz, a retired physics teacher at Waterloo Oxford District Secondary School, Waterloo ON.