Yes, their basic certificate isr free.
From their FAQ:
90.) Why are Class 1 certificates free?
The philosophy of StartCom is guided by the principal that our services are charged according to the effort we have to invest. Since Class 1 certificates are domain and/or email validated only and the process is performed mostly by electronic and automatic means, StartCom doesn't apply any fees for this type of certification. StartCom started the certification authority a few years ago with the goal to provide free digital certification and adopted a unique business model previously unknown in this industry.
I'd suggest you have a look at their website:
StartSSL Comparison Chart I really need the things that the free version doesn't offer. The only thing which I am in doubt is the validation level: what the class two or three comports than the class one?