otherwise https://www.gogetssl.com/ is probably as cheap as it gets.
From a security perspective, however, I think you need to meet some minimum standards to remain credible as a CA, and I think at least being willing to revoke certificates that may have been compromised for free and very quickly is one of those standards.
I find it difficult to support retaining StartSSL certificates as trusted-by-default in browsers given their response to Heartbleed and the consequent relatively high probability that any certificate ultimately depending on them has been compromised.
Sure, most of the complaining was due to the entitlement, but I'd be interested in a list of all the companies that complained about this and/or failed to pay for a revoke.
Looks like maybe StartSSL filled out their FAQ a little since then, but only a little:
The big problem is that since it's almost not used, browsers implement it but haven't done any job in making it user friendly (for example, you can see the certificates currently stored in your browser in Firefox by going in preferences > Advanced > Certificates > View Certificates > "Your certificates" tab, not exactly user friendly). Also (if I remember correctly) StartSSL implementation is not the nicest one as well, as you have to keep your tab open while they validate your account.
Proof of data integrity is typically the easiest of these requirements to accomplish.
A data hash, such as SHA2, is usually sufficient to establish that the likelihood
of data being undetectably changed is extremely low. Even with this safeguard, it is
still possible to tamper with data in transit, either through a man-in-the-middle
attack or phishing. Due to this flaw, data integrity is best asserted when the
recipient already possesses the necessary verification information.
Not only that, but I believe they refused to revoke the certificates in the first place without payment. So if you don't pay up, even if you go buy a certificate from someone else or decide to use self-signed certificates, an attacker could still use your old certificate to MITM your website.