If you buy it straight from the vintner in Germany it doesn't cost anywhere near €70, I can assure you!! In German, Eiswein (and it's slightly poorer cousins Beerenauslese and Trockenbeerenauslese) are usually sold in 37.5cl bottles, and from memory you'd pay about the same for one of those as you would for a 75cl bottle of good quality 'normal' wine. I've still got some from waaay back, maturing nicely. It goes a beautiful deep golden colour as it ages, and sems to get slightly sweeter too.
If the Eiswein is produced in Germany, you can be damn sure it's the real McCoy. The vineyards have to get approval from the powers that be to be able to sell it as such, they can't just bottle any old stuff and call it Eiswein, in much the same way as thy can't call any old wine Spätlese or Auslese, for example.