I have put together a system that will work within your budget.
http://pcpartpicker.com/p/3qnWF[DOUBLEPOST=1397306096][/DOUBLEPOST]
Yah though he is not going to get the specs that is needed to run a FTB Server from a pre build system under $300
For 4 people, yes he will. Absolutely so. Maybe not 10 players with tons of machines running.
As the OP says he will only host 3-4 at a time, it will be perfectly fine. The machine will be dedicated solely to running a server for no more than 4 people. He could, in fact, run a 4 man server on less than that.
Please take the time to read the entire post and get all of the information you need to make these sorts of statements. Not to mention a C2D at lower clock speeds far outperforms that A4-4000...roughly 35% better. If you think the C2D wont do the job, I am confused as to why you would suggest a CPU that has
even less horsepower.
I mean no insult here, but I really dont think you know what you are talking about in this particular instance. Im sure you want to help, but lets not send this man off on a journey he doesnt need to take with misinformation.
Edit: looks like you just ripped off this post from about 8-9 months ago and used it to suggest a server build:
http://pcpartpicker.com/b/ESz
I will refer our OP to this article, and caution him to leave plenty of overhead as FTB uses a bit more resources than your typical MC server. (which in addition to using actual experience, I have done when making my recommendations)
I will also caution OP to research in several places and compare recommendations - including my own - to other replies. The Internet is a great place to get help, or get screwed by someone who doesnt know but pretends to know. A lot of people are like car salesmen; they want to sell you something more than what want and need just because.
http://minecraft.gamepedia.com/Server/Requirements/Server