Could do it pretty cheap to be honest. id say 500$ could get you a good light, all your soil and pots, and adequate venting for a small space. You will have to shop around and plan ahead or you will spend more than that. HPS can be used from beginning to end with some supplemental CFLs for veg (imo). Also depends on what you already have. Youll need timer (a good one), thermometer, ph tester, nutes. All of those are optional I guess but HIGHLY recommended to have. Seeds can also be costly, they can also be free but if you want good genetics, you usually have to pay... I don't see how 300$ would get you everything