Okay. For the competitive deck, it's just teh ravagers and the skullclamps that cost the money. While the skullslamps you can't avoid, you CAN avoid using the ravagers (use Slobad, Goblin Tinkerer, or some of the Mirrodin commons that get bonuses for artifact sacced), although the deck power is decreased, it is still VERY powerful and can likely kick butt in Type 2 competitive play. If it's type 1...then good luck to you too (meaning they'll laugh at you before completely flattening you with their ultra-super decks of doom).
Type 2: It's the format in which only cards from the two newest blocks will be used (so Mirrodin and Onslaught)
Type 1: The format in which all sets are legal, but all restricted cards in type 1.5 (along with the banned cards) are banned (so type 1.5 is just restricting the cards rather than banning them outright)
Sealed Deck:
The sealed deck format is always constructed AND block construction. This format is arguably one of the most fair formats in Magic, meaing that you're depending on luck mostly (for sealed deck), and skill of what to put into a deck.
For the sealed deck format (in prereleases), you are given one tournament pack from the most recent block (it's Mirrodin for this one), and 3 boosters (some are 2!!!) 5th Dawn. You are given any number of BASIC LANDS to run in your deck.
With what you have, you have to make a 40-card deck from it. So from a total of 90 cards, you need to pick out about 24 cards to put into your deck, and the rest are ALL SIDEBOARD (meaning you can literally change your deck if you really want to during a match, although most don't do it).
Then after making the deck, you just play around in the tourney, usually just beating players and stuff. :P
Strat:
Take what you have an identify the Biggest bomb you can find.
Find cards that work well with this bomb.
Check your deck to see if you have enough to make this deck.
If so, you can then throw in your lands (about 17 is good) and make the deck. (aim for 40, you can overshoot by about 2)
Most decks have 2 colours in Mirrodin, you can splash (meaning adding like 1 card from a totally different colour) a third colour (note that you splash ONLY for cards that have a mana cost that doesn't have mroe than 1 of a specific colour. So like a splash on skyhunter Cub is okay, but a splash on leonin skyhunter is not. Usually ppl splash in green for artifact killing.)
Yes, it's about experience, but it's fun right now! and you will learn as times goes on. :P