I just got the Jund pre-con Commander deck and I was wondering if I can fine-tune it (of course on a budget). Would anyone help with that?

You're going to need to give us more detail than "help tune it." Specifically, answer as many of these as you can:

What are your favorite cards in the deck as is that you would like to build around?
Do you have any cards currently in your inventory that you would like to feature?
What type of strategy do you plan on employing (keep in mind EDH is more than just aggro/mid-range/control)?
How competitive is the group you're playing in?
Are you playing French (1vs1) or group (4+)?
Are there any rules specific to your playgroup we need to be aware of?
You say "on a budget" and that might keep us from proposing Gaea's Cradle and such, but what is your budget (ballpark)?

I could list a few more, but that should get you thinking about things and, with any luck, get the ball rolling.