Before I go into details about my bad experience, I'll just say that:
-the consierges are very nice :)
-the rooms are tiny
-going up the narrow stairs is very hard if you have a lot of luggage
-breakfast is good :) fresh croissants served with a hot drink such as hot chocolate, tea..etc.
-you can see the Eiffel tower from the front of the hotel. Also, if you want to save money there is a supermarket around the corner were you can buy food.
OKAY NOW THE BAD PART:
My ipod touch served as my alarm clock, and on my last day i left it on the bedside table. When i came back at 21:00 I discovered that it was no longer there. The cleaning lady obviously took it, since she has access to the room. They called her at home but she denied it, since there is no way to prove her guilty. I now realize that i shouldnt have left it on the table... but either way, the cleaning ladies should not take what doesnt belong to them :S remember to hide all of your valuables...

I stayed in Hotel Cactus but could not check in until 3 p.m. Petit dejuner was supposed to be included but I had to leave early in the morning. They would not give me coffee for the next morning. There is no elevator so if your bags are heavy, the stairway is treacherous. The locks on the doors do not work and neither do the hallway lights. The place is not clean. there is no reception area open where one can wait for a friend. They advertised for internet but there was none.

This hotel is good situated with Metro station just around the corner. Also Institut Pasteur is only a few meters away. But this are definitly the only good things! It is definitly not cheap enough for these dirty rooms! Everything is used up, it smells strangely and you wouldn't want to touch your blanket with skin. I do NOT recomend this hotel! There are a lot of other hotels in this area - no need to go to the cactus! The breakfast is not good and exept from one lady in the morning the staff is not friendly!

Clean, comfortable, friendly staff, but certainly not a modern or fancy hotel- exactly what one should expect for less than 100 Euros per night in Paris. I would stay again.