You have to rent a bigger apt to be able to do it, or you're sacrificing space. It's not costing you money right now, but theoretically it is.
Growing profits are determined by risk and labor, dealing by risk alone. Growing is a million times more work than dealing. Maybe it costs you $0.25/g to grow, but it's certainly taking you more than $0.25 worth of time at minimum wage to grow.
First of all, there is still work involved in dealing. You have to develop your connections, and deliver the product securely from point A to point B (or maybe A to B to C). That takes time and work, even apart from the risk. There are costs involved in terms of gas, phone, security, etc. If you're going to count time value in growing, then you have to count it in dealing too.
Again, the exact level of risk is highly dependent on the exact circumstances. Growing can less risky than dealing, but it can also be more risky. It depends on where you are growing, how many plants, under what circumstances, whom your deals are being made with, how big they are, etc, etc, etc. Big grow ops are potentially a lot more legally risky than small time private sales.
Growing certainly doesn't have to be a "million times more work" than dealing. If you're already tending a garden anyway, then growing might literally be as simple as throwing a few seeds in soil in your garden in May then harvesting them in October.
While its true that not every cost can be exactly measured in dollars, there is no "theoretical" cost; either something is a cost or it isn't.
In business there is a concept called "incremental cost", and that's what we're talking about here. That's cost incurred by doing something over and above costs you would be incurring anyway.
The classic example is you're a boss, and you have ten employees who each manufacture ten widgets per day for your company. Now you get a new contract, so you have your workers make twelve widgets per day. Since your employees weren't working to their maximum capacity, and since you're just using manufacturing capacity that you had but was otherwise sitting idle, you don't need to hire any more employees or buy any more machines to make up the extra output. In practice, the incremental cost to you of the extra widgets is ZERO, apart from the raw material cost. Not only are you making more money in an absolute sense from putting out 20% more output, your profit MARGIN has gone up too. . .since your labor and manufacturing costs are divided by a larger output you're making more money
per piece.
If you're growing in a space you would otherwise be renting or paying for anyway, then there is no incremental cost of that space for growing. For example, if you convert an unused corner of your basement into a grow area, the effective cost to you of using that space for growing is zero. You're just using potential space that was otherwise wasted. Toss a pot plant into the corner of your already existing vegetable garden, again, no incremental cost.
Yes, there may be additional costs of light, water, nutes, your time, etc, but those are different than space costs.
Now, lets say the space you want to grow in is being used for something else. Now the cost to you of using that space for growing isn't the same as the cost of renting it, its the cost of displacing whatever you were doing there first. That could actually be MORE than the rental cost of that space, or less, depending on what you were doing with it.
Lets say you are an MMJ patient and even though you can legally grow up to 6 plants, you don't need that many, and usually only grow 4 at a time.
Now lets say you decide you want a little extra cash and decide to grow some extra bud. Throwing another two plants into your existing grow may involve negligible incremental cost. Since you're already done all the work setting up the grow space, already have all the nutes, pots, etc, and since you're already doing all the labor on an ongoing basis anyway, the incremental cost of maintaining a few more plants is simply not significant.