Affordable macro for a77.

I have an a77 with the SAL1650 and 55300 lenses.

I would like to get into macro photography, but can't make up my mind regarding an affordable lens (read "cheap").

My 55300 can get some close shots at 300mm but just doesn't do so very sharp.

A beercan seems to be a viable option at around $150 on eBay, but is this a good lens for taking pictures of insects near flowers for instance?

Are there any other lenses anybody could recommend?