Mechwarrior 4: Mercenaries is free to download at Mektek and comes with all the additional mech paks, weapons and other toys. If you happen to own Crysis Warhead, there's Mechwarrior Living Legends, which is also free to download as well.
I bought and played Front Mission Evolved back when it first came out, and to be brutally honest I thought it was the worst 50 dollars I'd ever spent. The story mode is short and unoriginal, as are the characters, customization is pointless because rather than parts having their unique strengths and weaknesses like in Armored Core, different parts in each weight class just get better and better as you unlock them, and there's zero multiplayer community to speak of.
http://www.mektek.net/index.php/home/ar ... oads-r1204http://www.mechlivinglegends.net/