I know that Dollar Tree starts putting out their bags of bugs and other buggy things around Valentine's Day/Easter. They also have out stuffed caterpillars that could be nice for the little guys/gals. Plastic bugs could be buried in a sand box for a "Dig for Bugs" activity.
If you don't have mason jars, start collecting pickle/relish jars. Ask friends and family to help collect!
The blogger told that she got the green grass mats here. That's already a pretty cheap purchase, I think!
Also, I know that Dollar Tree carries the bug catching nets and boxes for $1 a piece (of course!)---Great party favors for each child.
Halloween always has spiders that you grab 50% or more off after the holiday. (Again, plan early to allow more time for deals. Trying to find spiders out of season is difficult.) Speaking of Halloween--- stores always carry wings and antennae for bumblebees and lady bugs. These could be great favors for a girl's party.
I see in the blog that one of the activities was the game "Cooties." That is always a "Black Friday" deal at Wal-Mart for $3-5.
If age appropriate, kids love to watch the move "A Bug's Life."
For paper cutouts, a cricut machine would be great, but if you don't already have one--- ask a teacher friend to use the die-cut machine at school to cut butterflies, lady bugs, and other insects.
During the summer time, all stores have "luau/summer" sections that have trays and platters in the shape of palm leaves, much like what she used. This would be another 50% deal to grab. You could also get green posterboard and cut out big leaves to lay on the tables.
Serve dirt pudding with gummy worms!
As always, check Oriental Trading. They have everything for party favors!