Ellen, wouldn't you be better off starting them in your basement or house? If the sun is out during the day, your gr.house will get very warm but it can cool down to the 20's at night. Without some heat, I think your seedlings would freeze.
Peggy

An inexpensive alternative would be winter sowing. Check out the forum and faqs. Ma nature does most of the work, costs are greatly reduced and seems to create less dreary winters.

I agree about ws'ing but a small greenhouse like that could work. Heat mats and such could help and like it will soon be above freezing each nite and in the 60's and 70's during the day.

I have seen nice little gh's on the web that are not too expensive. . GL.

Check out the greenhouse and garden structure forum. I just saw exactly what you are thinking of. Comes from harbor freight. the poster has many pics of it as he is assembling it, with a final pic of finished product. Should stand up to our climate and snow.

Just a plain old coldframe might be all you need. I have had very large vegetable and flower gardens and grew all the seedlings I wanted using a home made cold frame. The best thing was the little automatic venting device that cost about $40.00 that keeps the plants from getting fried. I had an electric mat in the coldframe as well, but I have read you can use a votive candle for a little frost protection. A combination of winter sowing, a coldframe, some temporary frost protection (little tents/hoops covered with some spun fabric), milk jugs, whataever) could work for you. Another thing nice about coldframes, is that you can move them, or even remove them, from the garden when not needed. If one isn't enough, you can always add more. Less of a committment than a greenhouse.

Thanks to all of you for your sage suggestions. Once we have a house that will accomodate a good veg. garden site, I will look at my options and see what works best. I was thinking it would be nice to have the greenhouse double as a workspace, but if I have sufficient garage space, a potting bench might work as well along with a cold frame (and I'm going to study up on winter sowing.) thanks again!!

I've been using a greenhouse in MN for many many years to get a head start on spring.

I started with a 6X8 collapsable model. When I was finished with it in the early summer, it was collapsed and stored in the garage (rafters) for the rest of the year. Just a couple of years ago, I gave it to my sister in law and she is still using it (thing must be about 10 years old). It's been taped now on several corners and the plastic cover will likely need to be replaced in the next year or so. But it has held up well (since it got put away during the winter).
Typically, I'd start using this portable greenhouse by April 1st (sometimes earlier). The important thing I needed to do was to remember to open the vents in the morning before I went to work and then close them again at night before the sun went down.
To help even the temp at night, I found a 55 gallon drum of water really helped do the trick.

I know use a permenant structured greenhouse and the polycarbonate has held up very well (going on 4 years now).

So, greenhouse in MN?...Definitely :)