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First of all, you should get a => Half Fare Travelcard, so each trip to Zurich will cost you approx. 40.- instead of 80.- (assuming a point-to-point ticket from your home to the Uni/ETH, adding the ZH city ticket option for free bus/tramways in entire Zurich would add +2.-). So the total ticket cost just for commuting to the Alma Mater would be approx. 3300.-
The break-even point for a GA at regular price (3995.-) is however around 5500.- tickets (half fare price) per year, as only starting from this ticket turnover amount you’d gain more than the 30% discount of the HF+ 3000. Also note that with the GA, e.g. a trip to the Jungfraujoch would cost you an additional 100.- from Grindelwald/Wengen to the GA costs, while with the HF+ you would deduct those 100.- from the HF+ credit, but you actually paid less (up to 30%) for that.
Now this break-even point is calculated under the assumption, that the HF+ would be renewed after the first 3000.- credit are used up. You didn’t state whether you’d leave Switzerland after one year or you’d add another year.
Nevertheless, for only one year, a Half fare Travelcard, a first HF+ 3000 and then maybe a HF+ 1000 next spring (190.- + 2100.- + 800.-) would still be cheaper than the GA. It really depends on how long you’ll stay here and how much you’ll spend on the weekend leisure trips (+ occasional local public transport in Basel).