If you do have a price that low, then you should always offer 100% commissions. If you go any lower, it won't seem worthwhile for people to promote. Then you can say on your salespage that "you can make your investment back with a single sale!" or something similar. Sure you'll be losing out on cash, but your list should grow pretty big.
You would get a much bigger list by getting a few partners and selling it to their lists in addition to whatever marketing efforts you put in rather than giveaways. A typical giveaway, depending on how high your gift is listed, will get you 50-500 subscribers (roughly). Having a viral campaign where everybody gets to earn 100% commissions will result in more than that.