How to decide on a new Hard drive for macbook pro
I would head on over to a Mac Specific reseller like OWC MacSales, RamJet or   where a company has figured which models are the best to sell based on your specific model.

http://www.ramjet.com/sata.asp

You will see that you have many choices for well under your budget. Also you are spared the SSD/HD decision since your size/price constraint means the quality SSD are not priced in your range.

When you buy from someone that has done the work, they will support you and help you should you run into issues. Get a few options and make the call if you want to buy from someone that will also answer your questions or if you are comfortable buying a community part and ensuring the firmware works, etc...

Since RAM is so easy to swap, you really don't need to include it in the HD exchange other than your budget may be fixed. It's hard to give advice on that front, since your budget is yours and not something that transfers to an internet forum where this question and answer might apply to anyone. Without knowing your specific model and how much RAM is in use routinely based on your apps, it's not possible to advise what the most cost effective combination might be.