The kits that cost the least tend to suck when it comes to BanDai kits... (They don't look THAT bad, however... But still, not perfect... )
Like the 1/144 SEED no grade kits, which I'd think are about $3-$5 each, but have limited posiblity (They're "Tradeing Kits" or something... I own the BuCue kit from the series, and it looks good, but you really only get one good pose out of it... )
And then you have the 1/144 Wing, G Gundam, and Gundam X kits, which aren't TOO bad, but they still need work to look good... (I wouldn't pay more than $5 for them, but I dunno how high their prices are now... )
Then you have the HGUC 1/144 series of Gundam kits, which are the best, but they cost more... (Like $8-$20 or so... or like $200 for the HGUC Dendrobium, but that thing's huge, anyway... )
The higher priced kits, the 1/100 MG and HG kits tend to cost around $20-$70+, so I doubt you want those...
Anyway, go to HLJ.com to check out direct from Japan prices, or perhaps GundamShop.com, whos prices aren't too bad, though they're in NJ... There's also HobbyFan.com, but I never bought Gundam plastic kits from them... So I dunno how their prices are, I'm going to check, though...
Any other questions, feel free to ask me! (I should be able to answer them... )