As westbud said your setup will be a factor (poor setup = poor growth = longer time to preflowers)...strain is also a factor, some show sex earlier/later than others. I had three plants from various bagseed and they did not show sex until about week five.
Setting up a grow spot for one plant will not cost you much money at all, especially for the first few weeks as you don't need much space and can probably rig something up from stuff you already have, don't need a ton of lighting (2 26W CFL's...$5-6 for a 2-pack, depends on brand. Although by week three adding two more would be a good idea), don't really need any nutes if you start with a decent soil mix (store-bought or home-made), and if you can be around and remember to turn the lights on/off at the right time to avoid buying a timer (although those are quite cheap too).
Although I do have to question how you plan to make money off of one plant...at least not the first harvest as you'll have to cover the costs of purchasing all the equipment. If you don't set it up properly you won't get much yield meaning no profit. If you set it up properly and starting from scratch you'll probably need to produce at least half to a whole ounce or more to recoup your investment costs (lights, timer(s), power strips, pots, dirt, nutes, fans, electricity, and so on) depending if you go CFL or HID lamps. Just a rough amount off the top of my head. But if you're looking at cloning it (you mentioned using this seed as a base) the returns could be pretty nice but it may take 4-5+ months to see any profit as it will take ~3 months for the first plant to mature and ripen its fruits and the clones will take a few months themselves to take root, veg, and then flower to harvest.