Buying old units

[GamerSince1998]

I currently own a very old system and thought to have a new one. Well, the i-3 or so processors are quite very expensive ( If l add the whole system ). So is buying used processors or Graphic cards etc. fine or they will suck at work? Although l know it depends upon its past usage but still I would be thankful for a reply on If i take used units will they still work fine?
And if no can I get a good specification in 300$s ?
* Well living in this generation and asking for spec is 300$ is shit but still .. I don't care on resolution or running the games on low or very low, Just wanna run them *
Plus are Dual Core processors fine for low-end gaming? I think the Core 2 Duo processors are discontinued in my country, only used of this type.
Thanks.

 

[C12Friedman]

I might suggest a very basic part replacement like this as one option
PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: AMD A8-3870K 3.0GHz Quad-Core Processor ($89.69 @ SuperBiiz)
Motherboard: Gigabyte GA-A75-UD4H ATX FM1 Motherboard ($79.48 @ OutletPC)
Memory: GeIL EVO POTENZA 8GB (2 x 4GB) DDR3-1600 Memory ($63.99 @ Newegg)
Storage: Western Digital Caviar Blue 320GB 3.5" 7200RPM Internal Hard Drive ($39.45 @ Amazon)
Optical Drive: Samsung SH-224DB/BEBE DVD/CD Writer ($15.00 @ Newegg)
Total: $287.61
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2014-04-18 10:21 EDT-0400)

Your pricing would likely be a little different but may be near that of what I linked. You would need to reuse your current case (hopefully it's not a small case) and your PSU and I do not address an Operating System at all (which will need to be added). I included an optical drive and a hard drive (a small one) since they are SATA and if your old system is older than 5 years it will likely be running IDE. If your old parts are SATA, you could reuse those also (I'd still recommend a new hard drive though)
It's not a great build but should get you playing most games (some at low resolution)

What are the specs of the system you currently have (your very old system), there may be upgrades for it that are a better value for gaming