Three complete greenhouse builds, every item priced and linked
The short answer
Most greenhouse buying advice sells you a structure and stops. That is the wrong end of the problem. A greenhouse is an envelope, and an envelope on its own does almost nothing: it holds a few degrees above ambient, it cooks anything inside it on the first sunny afternoon nobody is home, and it dries out a container crop in a day. What produces a result is the system of heat, ventilation, light, water and propagation gear that goes inside it, and that is what these three build lists specify.
Each build below is complete. Every item is priced and linked, the groups have subtotals, and the grand total is computed from the same catalogue that prices the rows, so the number at the bottom of a build page and the number on this page are the same number by construction rather than by proofreading.
They are also genuinely different structures rather than one list at three prices. The $390 build has no outdoor power at all. The $1,527 build runs on one 15 A circuit. The $4,228 build assumes a 240 V supply. Those three constraints, not the budgets, are what actually separate them, because the electrical supply available at the site is the single hardest limit on what a greenhouse can do.
Which build is yours?
Answer one question first: are you extending a season or changing which season you grow in? Season extension means hardy crops harvested earlier and later, transplants started at home, and no reliable minimum temperature. That is the beginner build, and it costs $390. Growing through winter means holding a floor temperature regardless of what the weather does, which requires heat, control and a sealed envelope, and starts at $1,527.
The second question is what power you can get to the site. This determines the ceiling on everything else. A 120 V 15 A circuit supplies at most 1,800 W, and a 1500 W heater is already at the continuous-load limit on its own. That caps a heated house at roughly 36 to 50 square feet in a cold climate. Past that you are into a 240 V circuit, a lower target temperature, or accepting frost protection rather than heat.
The third question is honest time. A greenhouse with no automatic vent opener needs someone present on every sunny morning and every cold evening. All three builds here include automation appropriate to their scale for exactly that reason, because the most common way a hobby greenhouse fails is not equipment failure, it is the owner not being there on the day it mattered.
The three builds
Size it before you buy it
The decisions behind the builds
What every build here has in common
Four principles run through all three lists, and they are worth stating because they explain several choices that look odd in isolation.
Automation before capacity. A vent opener costs a fraction of a heater and prevents a more total failure. Across all three builds, the item that prevents a loss is bought before the item that raises a ceiling.
Measurement before intervention. Every build carries a max-min thermometer or a logging hygrometer, because the overnight minimum and the afternoon maximum are the two figures that drive every other decision, and neither is knowable by standing in the greenhouse at a convenient hour.
Root zone before air. Germination and rooting respond to soil temperature, not air temperature. Heating a small bench to 78 F costs a small fraction of heating a house to the same figure and produces the same result, which is why heat mats and a controller appear even in the build that has no greenhouse at all.
Envelope before heater. Insulation, sealed door gaps and thermal mass reduce heating cost permanently for a one-time spend. A larger heater raises the bill every night it runs. In every build the recommended next purchase is envelope work rather than more output.
A note on the prices
Every price shown is the figure recorded at the time of writing, and greenhouse equipment prices move considerably, particularly on structures which are seasonal and frequently discounted. Treat the totals as the shape of the spend rather than a quotation. What does not move is the proportion: in all three builds the structure is roughly a third to a half of the total, and the systems inside it are the rest. Budgeting for a greenhouse as though the kit price is the project price is the single most common planning error in this hobby.