I'm currently taking post-bacc classes with SDSU's SLP Prep Program. It's online and it's like 8-9 classes total. You don't have to apply or anything, you just pay for the class. It doesn't give you a certificate, but it seems in the application process, schools haven't asked for a certificate or anything like that, they just want to see transcript evidence that the classes were taken.
I've been pretty satisfied with it so far, since it's just one year while other programs take 2 years. However, if you want to apply to some schools like CSULA or Northridge, they require way more units and SDSU's program won't be enough. I think SDSU's program offers 29 units.