are the kits still for sale?

No.

Kits were sold of about 4 years ago.

better off finding one with t16 conversion than a supercharged one anyway

T16 wouldnt give any power perfomance benefit over a 180 tbh. so better of with a 180 with the right mods.

well the T16 produces more power than the 180 and has more potential
If your willing to spend money on a super charger then a t16 is the way to go imo

A T-16 is an ancient lump and isnt that tuneable unless you have hefty pockets. I know people that a spent thousands on a T series to simply gain 80bhp. Not worth it.

So what is recommended for a 250bhp+ ZS for least amount of money spent?

Ive seen mildy modified t16's burn past focus st's
hmm I dont know maybe it was a strong engine or something

I can agree with you on that on the fact that my missus built her ZR Turbo and now owns an ST lol. HP wise it was similar but the weight ratio was in the MG's favour

yeah 18k worth of focus st beaten by a rover 400 estate turbo

the st owner was not best pleased lol