Well it seems I have been summoned here! ;) Val has given you good advice already. As she says, I am an artist, and I largely work with acrylics, assemblage and illustration, but I do use some watercolour, so I will add my input.
Watercolour is definitely less expensive than some of the other media, and especially since you are just starting, you will not need to worry about getting the highest quality supplies. The higher the quality of supplies the better the painting of course, but I assume that since you are starting, many of your paintings will be practice pieces, so you won't want to spend a fortune. Here are a few things to consider:
Paper: For beginners, medium-grain watercolour paper is best. It dries more quickly than course-grain and is easier to work with than fine grain. You can paint slowly on medium-grain and still not "wreck" or "overpaint" the piece. To save money, buy smaller sheets of paper (like letter size or slightly larger), rather than the large canvas-like sizes. You can also get away with buying generic or low-end brand pads of watercolour paper, the kind you find at a druggists or supermarket. Just make sure it says "medium grain".
Paint: Watercolour paints come in many forms:
Dry round disks in pallettes, to which you add water: Usually these are of lower quality and meant for beginners, but there are some better quality dry paints available.
Watercolour pencils: good if you can draw well, since you draw, colour, and then add the moisture with a wet brush. General's is a good quality, but not outrageously priced brand, if you are interested in these. You do need to be careful with colours running together, however.
Moist tablets in tins or pallettes: usually used by professionals, and more expensive than the above 2 choices.
Creamy paint in tubes: again, mostly used by professionals. However, there are decent quality generic brands of creamy watercolours, so price is not as much of a consideration.
Liquid paint in jars: used mostly by professional illustrators.
Brushes: Here you should splurge if you can. A cheap brush makes even the best paint on the best paper look shoddy. These days there are some very good synthetic brushes, but I personally prefer brushes made with real hair. My ideal brush set for watercolour is 5 brushes: three sable hair brushes in sizes 8, 12, and 14, a size 24 ox hair brush, and a wide Japanese deer hair brush. Or, if the thought of real hair makes you squeamish, a good quality synthetic brush set, using the same brush sizes.
It would be ideal if you have a large department-like art store such as
Michael's near you, as this tends to be cheaper, especially for a beginner, than buying from a small art shop. Michael's has a wide selection of good quality generic art supplies such as paints, brushes, easels, paper, etc. I would also suggest that you go to the library and borrow some books on watercolour painting techniques. You may find that you'd like to try some painting on your own before joining a class.
I'm including an attachment of a watercolour illustration which utilizes watercolour pencils, creamy watercolours and a *tiny* bit of acrylic. It's not typical of watercolours but it shows that there's a lot that can be done with watercolour. My favorite watercolour artist, other than the classics of course, is the Asian illustrator
Jimmyspa. His site appears to be being re-vamped at the moment, but it is well worth bookmarking to look at later. You may also consider the Asian watercolour technique helpful... many beginners find it easier than the western styles and the results are quite beautiful! Try googling "Chinese painting techniques".
Good luck to you, I hope you will love painting as much as drawing!