Im new too and have pondered this question much myself, it seems the soil I use has enough N for my 6 week veg cycle but not enough of the PK nutes....like yourself, Im trying to do inexpensive grows yet still produce decent plants for my pleasure....I love ebay and so far have found a switchable ballast 400w MH+HPS, 160 bux includes reflector, ballast, cords and 2 bulbs...got 3 gal planters at home depot for 3 bux each, miracle grow moisture control soil a HUGE bag for 14 bux, I got Blue Mountain Organics Flower power on ebay for 13 bux with shipping....so Im growing about 10 plants at diff stages and have only invested about 225 bux and have good results and high hopes...u can check my journal for pics etc...
what bloom nute are u considering? I have heard of so many and dont know when to believe the hype and when not to...it was tough choosing 1 when there are many out there. Good luck and peace, puff and pass!