One thing I noticed when going to your site was that it was a bit text heavy and doesn't have enough images. Images tend to increase conversions based on my experience. I'm certainly not an expert in the credit niche, but I think you need to take a look at some other landing pages and see what they're doing.
Here are some to look at:
Credit Cards - Compare Credit Card Offers at CreditCards.com
Best Credit Cards - Compare and Apply Online - CreditCardGuide.com
Credit Card Applications - Apply online for credit card at Credit-Land.com
Also, I think your color scheme is a poor choice for converting credit offers. Again, take a look at what the other guys are doing. For the most part, their landing pages are bright and airy.
I know you have a limited budget, and credit keywords are tough to get cheap clicks for. However, PPC is going to be your best bet for targeted traffic that's going to convert. Also, don't be afraid to try some different offers from other networks. You might be surprised how much of a difference you'll see with conversions across different networks.
As DruSam and others have stated, never give up. Make some changes to your landing page and see if conversions go up. Try some site-targeted campaigns through Adwords and fire up MSN AdCenter and Yahoo! if you're not already doing PPC there. If all else fails, branch out and start a new project in a completely different, less-saturated niche.