Yes, and those limits are different for the Direct and Guaranteed program. You can find those limits, and all other pertinent info here: http://eligibility.sc.egov.usda.gov/eligibility/welcomeAction.do
Starting Score: 02/2013 606(TU-myFICO); 647(EQ-CreditExpert); 578(EX-CreditExpert) 
Hypass what part of south carolina are you in? I know for kershaw county sorta right outside of Columbia the income limit is 74,000 and some change I believe. I'm also trying to go this route but my score doesn't quite meet the 640 requirement that my lender is requiring. And you might wanna look at the SC Housing Authority website and if you don't make an extreme amount of money I believe 45,000 and lower they give you a forgivable 8,000 down payment assistance for new construction.
Congrats. Is the property your looking at eligible for USDA too? I wish you luck though in going this route. It seems like the least expensive way. Hopefully nothing goes wrong for me and I can do this sooner rather than later.