Fortunately I was able to go to Tel Aviv for a few days in order to search for an affordable accommodation before my actual stay. I took a hotel at Rothschild Boulevard since I wanted to stay in the city center.
For that I took the bus … which was a little adventure in itself. Apart from the Arabic numbers, everything is written in Hebrew, and the buses do not always go the full track. After accidentally being stranded at a mayor train or bus station, which happend to me twice going back into town, I had to resort to asking around to find my way back to the hotel. Luckily, the locals are very friendly and most of them understand English.
Most importantly, I managed to make a few appointments via Internet and meet some landlords and residents. It looks like I will get a sublet directly at Rothschild, near all the bars, restaurants, theaters, museums, and just 10 minutes from the beach.