BMW 330i would be your best option for R100k.
Other options would be the 318i Individual for fuel economy. I easily get 700km+ on a full tank with the aircon on and driving normally/spiritedly, but the maintenance on one out of motorplan is not so lekker.
330D would be the pick of the bunch but afraid of servicing/turbo/injector failures long term
Or use the R100k as a deposit on an E46 M3