Talk to the people at your post office. They would know the options and be able to make suggestions, which may vary slightly depending on where you are shipping from ...or to.
Common sense should be your guide. Many plants can take shipping fine, however some of them you will want to get there as soon as possible, especially when shipping in the winter or during extremes of hot or cold.
The postal employees should be able to tell you how long a package should take to get to its destination, depending on how it is shipped (and this may change depending on where it is going). This info should help you decide if it is worth the extra money or not.
Indeed some plants are hardly worth the cost of shipping, however that is what we all have to figure in when trading or ordering plants and things. Even ordering from a company gets unreasonable sometimes, when shipping is added into the price.
To me, I take this into consideration when ordering things or making a trade. Usually if I am trading for something, it is a plant that I want, and so the extra money is worth it to help insure its safe delivery to me.
I have sent plants at slower than "Priority", however I made that decision carefully. It is not that it can't be done without harming the plant, but again you ought to check with the folks at the P.O. to find out their estimate of how long it will take to arrive at its destination.
From what I have found, the difference in cost is usually not enough to bother.
An extra 4 to 8 days (or more) sending something "book rate" will save you a bunch of money, especially if you are sending a lot of stuff, however having a really nice H.G. Ceph or some rare Sarr hybrid sitting in a box for over a week might be enough to stress the plant out just enough to kill it or make it suffer and need a longer recovery time.
Sending a common VFT or Dew isn't a big risk however, is it. But then, if I am sending a few plants to someone in trade, I don't want to be sending them a stressed out plant either, no matter what it is. If I have to end up sending them a replacement, it will likely add up to more than having shipped it better the first time.
Don't get me wrong, I do agree with you in may ways and there are a lot of times when I would like to ship things slower (or have them shipped to me slower and save some $), and just take the risk. Sadly, that usually isn't an option.
I would simply suggest using a bit of common sense concerning this. Also, consider doing to others in a trade as you would have others do to you. When setting up a trade, why not ask the person how they plan to ship things, and how they want things shipped. If you both feel the same way, then no problem at all.
But if they want their plants shipped to them the fastest, safest way possible, would you still ship their plants slower/cheaper? And if their plants die (even if it is
their fault) they might blame you and your shipping methods! Can you afford to get the reputation of not following thru as agreed?
Again, I think the best way is to either ship the fastest and safest way you can, or be sure to openly discuss shipping options when figuring out your trade with someone. I myself wouldn't mind discussing options with someone I am trading with.
And keep in mind that no matter how common or inexpensive a plant may be to you, to the person you are trading with, it could be the plant they have been wanting for years! So value is not always the same for all of us.
I don't blame you for wanting to save some money. Some plants and trades I don't bother with for that very same reason. Even some freebies are not worth the postage to me, so I don't bother with those. Indeed postage is getting higher and higher, and for some of us with tight finances, it affects the choices we make.
As I said, for myself, I would be open to various shipping options (Likely I would base my decision on many variables, the first of which is: "What's in the box"?). However in general without open discussion about shipping options, when trading with others I like to do the best I can for them. And that usually includes shipping priority mail. It is not that I always think it is needed, but I believe a lot of other people do.
Good luck!
Oh yea, And great job on the "numbers" Not a Number! (Did I just say that?!)
Although from the look if things, I would have difficulty fitting 70 lbs of plants in one of those Priority non-flat rate boxes! But then shipping plants potted up in wet peat and sand does add up!... but again I think the sizes of the boxes are figured to make sure they don't fit pots too well! Ah, yet another reason to ship plants un-potted/bare root!