Almost any speedcube can last you a long time if properly taken care of. It depends on whether you plan on just buying one speedcube and that's it or if you think you might buy at least 3 or 4 different ones and see what you like better. Because all the new cubes are great but you will like ones better than others and your choice will be different to mine or to other cuber's choice.
If you just want one cube then I'd recommend to get one of the more premium cubes out there, with good quality plastic, as it will last you longer and it can serve you well until you are beyond sub-10 if you can reach that goal. In that case I would recommend an Aolong v2, Tanglong, Meiying or Hualong (there are more, these just came to mind first). Or the new Aolong GT, of course. Any of these will cost you between $11 and $16 depending on the store.
If you think that you'll end up buying several cubes I'd recommend starting with some cheaper / older ones. They will be almost equally great and capable of sub-10 but maybe corner cutting is not as good as with the other ones or plastic will be a bit less durable. For example, I used a YJ Chilong as my main for more than a year and it is still in great condition and it is still a great cube that gets me as good times as my current main. It even makes me be more careful and accurate when turning as its reverse corner cutting is not as good as with other newer cubes but that's what makes me come to it from time to time as well. Other recommendations would be the Thunderclap (cheap and maybe as good as the Along v2 but corner twists a bit) or the YJ Sulong (also a bit old and can be found dirt cheap). Also the Shengshou Aurora is a nice and buttery smooth cube but it is a bit sensitive to proper lubing and tensioning so I wouldn't recommend it unless you know what you're doing. You can find any of these for as low as $4.