Cheap cold frames
Before I had a greenhouse I grew my plants in cold frames. This method doesn't work for all plants only those that need a month's early start. I did this mainly with fast growing flowers.
What you need--
good soil in a planting bed near the house for extra heat and protection.
4 or 5 wire hoops--I used wire clothes hangers that I straightened.
A sheet of heavy guage plastic--the plastic that covers new matttresses or furniture is great.
2 sapling poles or scrap lumber--the poles are best.
a couple of good sized rocks.
I put my hoops in the flower bed so they were about 15 or so inches high. Then I doubled the plastic to fit over the hoops with enough to spare to staple to the 2 poles. Then I gathered the plastic ends and stretched them out and put a rock on them.
The plastic can be rolled up on a pole and put behind when the weather calls for it or you can fold back the ends and clothes pin then to the wire on cooler days. I found that just about every day it had to be opened a little or a lot.
I put the cold frame up 2 weeks before planting to warm the soil. I planted in rows right in the soil. When I transplanted to my flower beds I dug the hole, filled it with water and let it sink into the ground. Then planted my plant and covered the plant with an upside down pot and left it for 2 days. This lets the roots hit moist soil right away and shades the plant until it can recover from transplant shock.
I also make use of big clear bottles like 2 liter pop bottles, or milk or vinegar bottles. I cut the bottom out and set it where I'm going to plant--same as the cold fram a couple of weeks early. Then I lift it off, plant about 3 seeds, and water. I put back the bottle and remove the lid. The lid opening allows heat to escape and the bottle keeps the ground warm. On cold nights I may put the cap back on.
I also use row covers and garden blankets to cover on extra cold nights.
I hope someone can benifit from this.