The good thing about the Zaku is there are a plethora of variants that have be released and even some of the older kits can still be had.
If you want the most up to date one there is the HG Zaku II Type C / Type C-5 from the origin promotion or the RG MS-06F Zaku II if you want something more Intricate as the RG's have full internal frames.
Some of the older kits are still good although the articulation will be slightly more limited.
The HG MS-06 Zaku II production type that I'm building for Sci-Fi 4 is going to be your no frill basic looking Zaku
There are also the MS-06FZ Zaku II which comes with an alt head sculpt as well as Char's custom Zaku II that if you want one with a commander antenna, the J type here also come with an antenna option too.
If you want to do some experimentation there are the FG ZakuII's which pay homage to the original 80's kits that can be had for like $3-5 a pop and while the articulation is very limited can't beat the price if you want to experiment with battle damage or need extras for a diorama