There's no need for a big budget to get you started. The basic colors, that I still use today, are acrylic, high-gloss, spray paint cans of a brand called "Spectrum - Paint and Supplies". They have a low coverage which makes them suitable for shading for the more advanced painter. For more diverse and high coverage colors, I refer to Mtn 94. They are only available in a matte finish, but I always suggest to coat your final piece with, if preffered gloss, varnish. Besides that, Mtn 94's low pressure provides more control.
Surfaces to paint on are everywhere around you. All solid materials that, in an extent, do not absorb the liquid are suitable (e.g. cloth, wood, metal, plastic,... ), but some may require primer to minimalise the intake. I usually paint on cotton canvases that are primed prior to purchase, but spray painting on posterboard is just as usual.
The following is the most important. MIND YOUR OWN HEALTH. Both dustparticles and harmful propellant gases are released when using spray paint. Always inform yourself on the risk of the materials you use. I advise to paint outside or in the required ventillation and wear skin-, breathing- and eyeprotection.*
*Disclaimer: I'm by no means an expert nor am I responsible for any issues. Please refer to a specialist for reliable info.