Rank 1 gifts (love) yield 96 affection for 200 credits. Rank 2 yields 106 affection for 600 credits (not worth it). Rank 5 turn-ins from Treasure Hunting yield 144 affection. If you were to buy Rank 1 gifts you would need 104 gifts to get to 10,000 affection. This would cost 20,833 credits and with a 30 second cooldown and 2.9 second cast, would take about 57 minutes to get a companion to full affection. The exception is Qyzen who doesn't love any gifts.
Edit: Well it was a good theory, but it looks like you get diminishing returns at 2,000 affection. At 2,000 the Rank 1 gift yields 48 affection. I'm guessing it'll continue to diminish at certain markers.
I tried to give a male companion a courting gift after telling him I wasn't interested, and I got 0 affection. I guess they only work if you're actually courting!
So I found this today to help you get up affection with your first companion: http://www.madcastgaming.com/forum/showthread.php?6124-Esseles-companion-affection-guide. With Qyzen I get 455 affection, not to mention the 250 light side points. If you skip everything but bosses and unavoidable trash, it takes about 20 minutes. Something to note, pay attention to commas. I got confused but an example is for Qyzen, line 4 it says "1, x 1, 2" and that means 1, not 1, 2. I thought "x 1" was 2 different conversation options. Took me a few tries to get it right.