1) Would you guys just make the panels yourself?
yes I would . Get the dimensions,figure out the material needed to make
similair panel,plan out how you would fabricate it.
The satisfaction of doing it yourself and money saved (which you can than
spend on the new "tool"you have wanted) is well worth it.

2) Would you make the panels out of cedar, or mix in some other stuff for
the above grade detail (#1 pine, or something else) ?
Are you going to paint it? Than do not waste the money on #1/clear
material since knots will not be visable. Make a few calls to see what cedar
costs are in your area. Have you thought about using cypress ?
It will paint well and last for many years.
For the posts depending on what you are willing to spend. I have found that
cedar doesn't last that well in my area of WesternMass.but pressure treated
have out lasted the cedar post that were installed at about the same time.
You could also use hemlock as the post,treat the below grade ends with
paint or tar them if you are going to install in concrete.Another option is
put concrete footings with metal brackets for the posts to be bolted
to.Since this is going to be in the garden some plants around the post will
hide the metal brackets.
3) Where would you buy that quantity of lumber?
Cowls Lumber Amherst,Ma. Kicza Lumber Hadley,Ma. for the hemlock
posts (they will also custom size them if you so desire)
Forest Products Assoc. Greenfield,Ma. for the cypress.

Is your deer problem so bad you must get the entire fence done at once?
If it isn't I would built a section this year of wood and put in an electirc
fence for the rest.Than finish it off next year.You can always sell the
electic fence material pretty easily.

Take the time to decide if it is a project you want to do and have the
time to do it.If you have youngsters have them help you out. It will be a
project that they will remember for years to come having built a fence with
Dad.

Have fun