Holding the Line
Advance to Hangar C
Video Walk-through
Getting in and out of Hangar C quickly will let you avoid most of the SBD's.
The Trade Federation has had more time to deal with the upcoming hangars, thanks to the way they were able to keep you busy in Hangar B. Thus, there'll already be a droid dispenser waiting for you here when you reach it. If you move quickly, though, you should be able to get around it and disable the force field without having everyone die.
Unfortunately, the only way to reach the hangar is to pass over the upper balcony. Take the opportunity to heal up any members of your squad that need it; while they're doing so, chuck a grenade or two down below to destroy the explosive barrels. They're only going to cause problems for you when you need to pass through that area in a second. Disregard the placement positions on the balcony, as well; when everyone's healed, tell them all to form up and head down the ramp on the far side of the balcony to reach the lower level of the room.
When you're in, you'll need to command each of your squaddies to perform a task. One of them should be assigned to the snipe point just inside the room's entrance, while the other two will follow you to the other side of the room. When you reach it, command one of them to start laying a charge on the field coil, while the other goes to work on the console underneath the balcony, near the broken speeder. While all this is going on, get up next to the droid dispenser and start killing them as they pop out with your melee attack; this will prevent them from going to town on the guy laying the charge.
After you get the head's up from the slicer that the console's been hacked, though, get away from the dispenser; the speeder will shoot out towards it, instantly blowing it away. Pretty handy, that! At about this time, the field coil charge should be about ready to go, so blow it and start the retreat. An SBD dispenser will likely have dropped during all of this, but you don't need to kill them to move on, so leave your sniper in place and take the other troopers and head back to the ramp corridor, where the door to the next part of the level will have opened up.
Overwhelming Odds
Advance to Hangar D
Ok, here's where the real fun begins. Hangar D has been fortified with droid and SBD dispensers, leaving you with the monumental task of taking out an enemy that's entrenched and has the advantage of numbers. What's worse is that droidekas have been dispatched to monitor the hallways leading up to the hangar, meaning that you'll have to fight your way to the fight, if you get our meaning.
To begin with, you'll find a sniping position, then a room full of explosives and a breachable door, behind which lurk three SBDs. There are a few ways to deal with this situation: either you can place charges on all of the explosives, then command all of your guys to hide behind the sniping spot while you breach the door yourself, then lure the SBDs back to the entryway, where they'll get blown by the explosives; or you can breach the door, then use the cover on either side to destroy the droids with anti-armor charges or EC grenades. The first is definitely more ammo-friendly, but it's worth noting that you're going to find more of both EC grenades and anti-armor shells shortly, so if you want the quick out, just save your game and try taking them all down yourself.
Next up is another hallway that's completely packed with explosives. It's important that you don't move too far up the hallway here; instead, just start pointing your teammates towards the barrels and tell them to plant as many charges as is physically possible. You don't need to have a charge on every single barrel, but try to make sure that each small group has one barrel with a proximity mine on it, and don't miss the pair near the crates. Eventually, you'll notice some droidekas moving around the hallway nearby. When one of your teammates tells you that they're coming back, drop back behind the sniper spot, set Sev up to start blasting away, and watch the fun begin. As the droidekas come down the hall, they'll trip the proximity mines and get blown away. If they don't get hit, then your sniper will be able to take them down; you can help out by hitting them with EC grenades or your blaster.
When the droids stop coming, grab the AA rounds from the hallway and head down to the bacta dispenser. There are a few SBD's in the hallway to the right, so use the AA gun to blow them away, then retreat down the leftmost hallway to find yet more AA rounds and some EC grenades. When you're ready for the real fight, save your game and head through the door behind the wreckage of the SBDs.