I've heard good enough things about the Hydrofarm that I'm thinking about picking one up to replace my 500R, not that I've had any issues with that one, but the digital display would be nice to have. If your budget is around $30, I'd say that looks like the best bang for the buck. I'd go for it...
I understand that Johnson and Ranco may be better, but when the OP has clearly stated that $30 is about her max budget right now, I can't say that telling her to save an extra $50 or $60 (essentially TRIPLING her stated budget when she's explained that she doesn't have a job right now) is very constructive or helpful...