Newegg used to be really good, but now you need to be careful with newegg now. Their RMA policy is really horrible and should you receive a dead product, it is a huge hassle to return it. Amazon on the otherhand has free shipping unlike newegg and 'no-questions-asked returns'. If Amazon has the same item, you should always go with Amazon over Newegg.
HDD-wise, because of the flood last year in Thailand where all the manufacturing centers are, the price has gone up around twice as expensive. I would wait getting a HDD until after summer when the manufacturing centers are back online and the price goes back down to normal levels. Of course, if price is no object who gives a shit. The best HDDs are minimum 7200rpm Western Digital. There are different classifications so depending on what you need the HDD for, you want to go with BLACK, BLUE, GREEN.
Generally, blacks are for games/performance, blues are for standard users, greens are for mass storage. I only use black but you may find different uses.
The flood did not effect SSDs because those are not made in Thailand, but SSDs are not good for continual write/read that a studio machine will do.
As for ram, DDR2 ram is expensive nowadays because they aren't made much anymore. For example, you can get DDR3 ram provided your motherboard supports it 8gb for 40$. I would advise looking into your motherboard and seeing if it is compatible with DDR3. If it is not, I would also recommend looking into purchasing a new motherboard (You can get really high-quality Intel Mobos for 80$ these days.)
My guess is that it sounds like you are running an outdated Motherboard and CPU combo which makes upgrading with the compatible hardware far too expensive. Since the new IvyBridge Intel CPUs just came out on April 27th, the last generation SandyBridge is going pretty cheap. You can pick up a solid quad core SandyBridge CPU and a solid motherboard for 170 - 180$ for both and it will make all you future upgrades easier.
SOO if your budget is $300 and if you go with a new CPU + MoBo + DDR3 (8gb) + HDD, it will probably only be slightly more expensive than upgrading current compatible gear AND you will most likely see a 1000% increase in performance.
I know it is a wall of text but I wanted to let you know all your options and what they would be. Of course, it would still be cheapest to just purchase the DDR2 and a new HDD right now, but you will eventually have to upgrade again.
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Crucial DDR2 you need two of these, same exact price, but amazon comes with good customer service:
http://amzn.com/B0011A4UZE
vs.
http://www.newegg.com/Product/Produc...82E16820148160
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Western Digital Caviar Black 1TB:
http://amzn.com/B0036Q7MV0 136$
vs.
Western Digital Blue 1TB:
http://amzn.com/B00461LT6S 99$
vs.
Western Digital Green 2TB:
http://amzn.com/B004VFJ9MK 119$
As you can see the Green offers most space but it's not for performance, meaning, if you will be recording onto the Green, you will have problems. If it is just for storing multi-tracks, the green is perfect. Again, I personally use Black even for storing movies because but the green will work just fine.
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Let me know if you need additional help~