Start up infrastructure cost are a big one.
My light shelves and fixtures were probably $500 which will hold 16 -10x20 trays
First year of pots, trays, nutes, soil/medium, heating mat, timer, and the likes was another maybe $500
Then there is heating expense, the first year, ~$30 x 2 months.
This year I bought them into a heated utility room.
Light expense ~$20/ month.
Second year, I've bought $60-80 worth of Ocean Forest soil.
And another $200-300 in soil building components. This is getting into material for the outdoor space as well.
$100 in pots and trays this year in moving toward a 3.5"deep pot and 5" pots and getting away 2.5" from for peppers.
This yielded in-ground plants of about 115 peppers, 18 eggplants and maybe 75 tomatoes. Plus a few odds and ends, kale, chinese greens, basil, lettuce and onions.
Starting quickly like I did cost a little more. You can scavenge and find better deals by thinking ahead.
2015 I'll still buy a few amendments to construct more potting soil. But if you have the room to make dirt, there's no time like the present to start.
Build a wire screen to fluff it up nice. Start worms. Start composting. It's way cheaper if you're going to be using more than 6 cf of container medium per year. Otherwise I'd be tempted just to buy a high grade mix off the shelf at a grow shop.
So 2015 and there after, my guess-goal is to spend less than 300 dollars on all garden supplies and electricity yearly. That would be to maintain and plant a 60x100 row plot that includes 300' of raspberry canes, about a 1000-1200 sf of raised beds, a little row strip ~6'x 60', and 18 young semi-dwarf fruit trees.
Everybody has a different scale. Peppers are my primary focus but I grow and preserve lot of other things too.
So let's say 2 years of plants -450 nightshades only- total expenditures from seed to plant out only, about $1600, or 3.56 per plant or segregated cost of
265 peppers for both 2014 and 2015 equals about $945 including infrastucture.