Hello, I am building a 50 card Return to Ravnica deck. It is a small tournament among about 20 of us and we are all using Return to Ravnica cards. I need to build a deck with only these cards.

http://deckbox.org/sets/447902

Populate is a popular strategy among them, any advise or suggested builds are greatly appreciated.

Hello, ^__^.

I'm new to this site and would love an second opinion on my deck as well as experienced guidance to optimize and improve it.
I'm playing this deck with a two small groups of friends and it already holds it ground fairly well. I'd say an win loss ratio of 1:1. However, a few of my friends are studying winning tournament decks and are starting to build far cheaper knock off versions of them. So, I'm worried I'm going to start losing really badly.

1) What level of play is this expecting to see?  Are you going to play casually just for fun or are you taking it to competitive FNMs?  Are your FNMs full of top level players rocking tier 1 decks, or is it more of a bunch of home brews?

I have no intention of playing super seriously and entering tournaments. My friends decks are all worth ~$30 - $120. A few of them do select online shopping. I wanna try that.
They are mostly playing angel healing decks and overwhelm decks. They get out large 10+/10+ type creatures quickly. [Forgive improper use of terminology please.]

2) Do you have a format restriction/preference?

As a group we've restricted ourselves to Modern and are ignoring the ban list. [Any cheep combos guys? :3]
I would prefer if at all possible to remain mono red.

2) What are the win conditions of the deck?  Or, in other words, how do you envision the deck winning games?

I envision myself winning two ways.

Main approach: Rushing my opponent with cheep instant, sorcery and creature damage.
Secondary condition: Reaching the 10 infect counter and wining the game automatically. [Focused around my colossus]

3) If you were to imagine an ideal 4-5 turns, how do you envision them playing out?

I suppose a fair mix of land and cheep creatures for the first turn, sorceries and instants or the next few the engine that will cheat summon the colossus.

4) What sort of budget do you have for improving the deck?  It's easy to suggest that you add $400 worth of cards, but if you're only looking to spend $20 to make improvements then suggesting 4x Snapcaster Mage isn't useful information.

I'm looking to invest (try to stick close to this guy)$50 - $100 into this deck to make it a well rounded and very effective deck not just an intentional counter to my friend's decks.

http://deckbox.org/sets/447913
Here is my deck:

25 Mountain
1 Barrage of Expendables
4 Goblin Arsonist
4 Pillar of Flame
1 Rakdos Cackler
1 Shock
1 Curse of the Pierced Heart
4 Gore-House Chainwalker
4 Krenko's Command
4 Mogg Flunkies
4 Searing Spear
1 Sudden Shock
1 Young Pyromancer
2 Arms Dealer
4 Brimstone Volley
4 Flames of the Firebrand
1 Chandra, the Firebrand
1 Etched Oracle
1 Hellrider
1 Krenko, Mob Boss
1 Quicksilver Amulet
1 Pyromancer's Gauntlet
2 Thunderous Wrath
1 Blightsteel Colossus

Total: 74 

TL;DR: My deck is pretty remedial and needs a tune up, for less than $100