The engineering profession in Warlords of Draenor gives you access to three crafted pets, which are easy to buy on the auction house if none of your toons is an engineer. Personally, I'm always strapped for gold, so I took the time to craft my pets on my alt (my rogue is an engineer).
The pets are "gated" in a way because they require a BOP engineering material called Gearspring Parts. You can only make a handful of these parts each day, and each pet requires 50 or 30 Gearspring parts, in addition to another crafting material. However, as long as you're patient, it shouldn't take too long to craft all the pets, as long as you're not in a hurry to make your engineering goggles!
The Lifelike Mechanical Frostboar is a pretty awesome pet because it's not a common shape (it's not like you have 1,000 boars in your pet menagerie like you do snakes, squirrels, and rats!). You'll need 50 Gearspring parts and 40 Sumptuous Fur to make your Frostboar.
The Frostboar's abilities feature a variety of damage types including Mechanical damage, Humanoid damage, and Beast damage. He also has the Decoy ability (very helpful in many pet battles), as well as a heal that heals 100% of the damage dealt.
Your next available engineering pet is the Mechanical Axebeak, and he's easier to make than the Frostboar with just 50 Gearspring Parts required.
Interestingly, the Axebeak is actually a Flying pet even though it's crafted by engineers. The Mechanical Axebeak deals Flying, and Beast Damage, and he's also got the Decoy ability, just like the Frostboar. He also has Hawk Eye (which is a crit chance increase), which I feel is a "meh" talent.
Your third pet is the Mechanical Scorpid, and he's pretty easy to make with just 30 Gearspring Parts and 10 Blackrock Ore (which you should have tons of if you've been farming your garrison mine!).
You've probably alrady got a few scorpids in your collection of pets, so you won't be wowed by the way this pet looks. It's a Mechanical that deals Beast damage, as well as some damage-over-time abilities.
Fortunately, the crafted pets available at the start of Warlords of Draenor are simple to make and require almost no farming. They just take a few days to craft the materials and are quite cheap if you make them on your own. After a while, they'll probably be pretty cheap on the AH as well.