I started getting into 40k around fall of 2006, so I've been playing for about 2 1/4 years. What got me into the game was how much fun I had with Dawn of War, with the Leman Russ and Bane Blade being the prime influences for my decision to play guard.
How much worth of guardsmen is going to be real tough to calculate, but here goes. I got these slowly, seeking out the most cost effective way and with an army list fully planned out months/years ahead as IG are NOT a very nice army on your wallet. 3 shock troopers (105), command squad (35), heavy weapon team (35), battle box containing shock troops, HWT, Leman Russ, and scenery (90), two three tank LeR squads (180), three LeR Demolishers (135), junior officer blister (12), 6 special weapon blisters (72), 3 Basilisks (90), 10 Grey Knights (84), 10 GK Terminators (125?), 4 cadian sentinels (120), 2 normal sentinels (50), Kasarkins (40), Chimera (35?), Hellhound (35?), Commisar Yarrick (17), Creed/Kell (20), 2 bane blades (180), lightning (120?), Hydra (60), Land Raider Crusader (55). Total: About $1695. Ouch. I got some of these at secondary stores to save about 10% on costs but I forget which models this applies to so I didn't account for it in the calculations. You Ork players are lucky, Assault on Black Reach gives ya a fully legal 500 point army for about $60, and World Eaters (Chaos dedicated to Khorne) can get a decent 500 points for $50 (One Khorne Berserker box and Kharne who is legal at 500 points). A bare bones Guard army at 500 points is $117 while a decent 500 point army is $186-198. Let this be a lesson to you; hunt down the battle boxes.