I have trained boxing for 5 months now, and have done SL5x5 for about 3 months
> If any, how do you like it? How is it with the 5x5 program? comments?

I love it. It is one heck of a workout. Doing StrongLifts will help you in ANY sport, but, that said, being 'boxing fit' is it's own unique thing, and you have to train it in and of itself seriously to get good at it.
> I want to get into it, kinda. First I am looking at buying a punching bag to release some stress
> but no idea where I should buy them or what price range is good? I tried googleing, so many styles and ranges from $150 to $1000 USD.
Before you buy anything: check out a boxing gym, and do a single workout there.
Then, you will a) know whether boxing is for you (in my experience it was a bit different than what I expected), and b) the trainer will tell you what to buy, before you waste money on stuff you don't need.
Also: don't bother with a punching bag yet, if you want to be a good boxer. First, get to a boxing gym and learn how to punch. Otherwise, you'll simply learn & reinforce bad punching habits.