First port of call is probably
Da Warpath for all things green.
As has been said, Orcs really do not lend themselves very well to budget armies. Your options include such gems as Savage Orc hordes at £18 per rank, units of 60+ Goblins and spamming buckets of Finecast war machines. If you are handy with green stuff / balsa wood and haunt eBay in the search for Skull Pass Goblins, you can bodge your way to a tournament list. If you cannot convert and want to take the cheaper options, your army list will suffer for it. They are an army that demands large investment of time and money to get right.
A big misconception among newbies is that they are a melee army; they are not. You cannot build an infantry swarm and expect to chop your way past all the Elves and Warriors at the top. Where Greenskins excel is in spamming massed numbers of cheap artillery pieces and forming one of the most infamous deathstars in the game for a grinding block. Other fun spinoffs include the '100 Goblin archers with 5+ Poison' list, Troll hordes and Chariot spam, but all lists will want to include a healthy core of war machines. As in, at least 4. They are dirt cheap and the only thing separating them from Dwarf ones is that they are worse in melee (and also no gunpowder options).
Staples of the list:
Savage Big 'Unz- Take 30-40 of the gits, get them a Shaman with the Shrunken Head, and bask in the glory of Orcs that will *demolish* almost any other unit in the game point-for-point. 3 Attacks at WS4/S5 and a 5+ ward save is scary for 11pts a head. Especially since it doesn't really cost you anything; you were always going to take 25% in Core, and you probably wanted a L4 Shaman as well. You only really pay 50pts for the Head.
Night Goblins- 3pts per model, almost T4 with nets, and Steadfast forever. You can fill out the front rank with Hero characters if you fancy winning fights.
Lobbas and Doom Divers- Cheap, long ranged and hard-hitting. Take maximum allowance every time.
Mangler Squigs- Some of the most destructive 65pts you can spend in any army. Fragile as anything, but they'll pay themselves back by turn 3 if they aren't killed immediately.
Wolf Chariots- 50pts for S5, scythes and they come in units. Again a unit that will pay for itself in the first impact.
Trolls- Costed like an Ogre, except they get S5 and Regenerate. Just keep them near the boss and you'll do fine. Also brutally hilarious in Horde formation.