Taking a quick look at the materials list, there are a lot of pieces at varying lengths.
If you want to use pine, you can probably save some money by cutting nice clean pieces out of the knotty pine (working between knots) with minimal waste, and maybe just pick up a few pieces of Select for the longer pieces that are required.
Another option between teh pine and oak, may be to use clear douglas fir. I had used that for some outdoor projects years ago and it stood up well over the years just being finished with water seal.
Don't know about the wheels from the egg, but I imagine that you could look for someone tossing out a lawnmower and grab the wheels off of that.
Pressure treated or not? Other consdierations aside, pressure treated has been dried and then had moistrue forced into it to carry the treatment within . Fresh pressure treated wood will have a very high moisture content and as a result will undergo a lot of shrinkage as it dries out.
Hope this helps. I'm sure others will provide more help too.
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