That's like asking someone to recommend you an automobile for $50,000 or less but not saying anything else about your needs.
There are dozens of options on the market, quite a few in your budget. But which one is the best for your personal needs? I have no clue.
Portable is any vaporizer you can use away from an outlet - some are larger than a 1liter soda bottle, and others are super-stealthy and the size of a pen. Some of them work better in party situations, some work well for solo use. Etc etc
Tell us more about your specific needs and how you'll be using the vape. Are you vaping for pain relief/sedation?