The short answer is no.
If you don't have a greenhouse, you can simply use a sheltered spot in your garden so your seedlings are protected from the worst of the wind and rain. And a simple sheet of horticultural fleece tucked around them for the frostiest days and nights.
The second answers is....but why wouldn't you?
Here's the set up that I have and love.
Now, I bought mine during lockdown from Aldi, at the time of posting this video, they didn't have any available, but do always check with them as they were great value.
So, here are some links to similar products on Amazon:
Here's the link to a similar mini-greenhouse in the video:
And here is the slightly larger one - these have gone up in price a little since I bought mine and the shelving arrangements change depending on what you buy, but this one is an example of plenty of others you'll find on Amazon.
Please, please please: weigh these down with bricks and concrete slabs and tie those shelves onto the frame with string!
As an alternative solution, some of our Floral Project members have had great success growing with these plastic crates. Simply put your seed trays or pots into these and put them outside. Take the lids off during the day and put them on in bad weather and at night - you can also always tuck some fleece over them all at night. Make sure the lids do come off so the plants are well ventilated.
Drill holes in the bottom for drainage or just be careful that after watering no water sits in the bottom of the box.
So.....a bit more fussing required here, but another cheap and cheerful solution!
Here are the photos from one of our Floral Project members, Anna, who has had great success using this as her 'greenhouse'
And another tip from one of our Floral Project members, Aimee who tried both a plastic greenhouse as above and using boxes: