let's say..
grade is works in this way.
1 / 144 HGUC, Seed, Seed Destiny, 00 = around late 10's to late 20's ( Xcept HGUC Dendrobium

and some new larger Kits. )
1 / 100 Master grade, Seed, Seed Destiny, 00 = middle 20's ( usally Seed or Seed Destiny. MG normally start at mid 30's ) to hmmm can go over 100 range
1 / 60 Perfect Grade = no more to say $$$ range.
there's more grade but i will skip it..
u have to search around to find lower price.
or if u find anything ask around at forum if they are reliable or not..
research research..

if u need tip for what i do.
pick a kit that look good to u then search on that one..
it will be alot easier then just looking for Gundam kit.
have fun hunting.