If you want to evaluate the cost, you have to include the development cost. 3rd party E-6 processing has to be added to the cost of the film. Kodachrome is normally with prepaid development, and you can also get Fuji Sensia 100 with prepaid development (at a Fuji Lab), and I think these two solutions will probably be the cheapest solutions. At least here in Switzerland, you cannot get any slide film AND 3rd party processing for less than the cost of a roll of prepaid Sensia or K64.
Having tried both, I personally don't like Kodachrome. The colors are wierd (to me) and it's tricky to scan properly due to its unusual construction. Sensia performs better, color and scanning-wise, IMHO. These two shots were Sensia 100.
Of course Sensia is a consumer-grade film, so it won't quite reach the perfection of Velvia 50 or Provia 100. But it's as good a consumer grade film as you can buy.
I've tried Agfa slide film, and the colors were too funky for me.
I would not go for 200 ASA slide film. The drop in performance between 100 and 200 is quite noticable.
Jwenting, I tried Provia 400F a couple of years ago. It was not bad at all. The grain and color performance is as good as a really good 200 film, or a decent 100 ASA film. But it is very expensive. I'd only use it if I had a lens that does not bring in enough light for a 100 ASA film.
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