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I think that 170$ is about the normal price for a 270X. Check the street value, don't just trust the price cut you are shown.

You are correct about not needing 4GBs right now, but you're also correct about wanting some room for the future. Expecially if you can get the 4GB one for the same price of the 2GB one. I think you might be using those 4GBs in 2 years, or at least have an option for textures that will use them in said time.

About bottlenecking: we need to know your current CPU and the one you want to buy. The 270X runs well on mid-range CPUs already.

About NVidia being more expensive for similar performance: they offer different features (PhysX, CUDA, good quality AA). If you want those features, I think it's worth the extra price. Otherwise not, of course. :)

Also check benchmarks for the actual games you'll be playing. While generally the relative performance is similar across the board, some games are way better optimized for AMD or NVidia. Check the real-world numbers.

Little addendum: if I had to pick a 100$ CPU it would be the AMD FX-6300.
A good runner-up is Intel's Pentium G3258.

At that price point I'd go with the FX-6300. It's a 6-core CPU vs a dual-core. While in games they'll perform in a similar way (the Pentium might actually be faster), in real-world use the 6-core would feel a lot smoother.
I recently went from a dual-core to a 4-core and I can vouch for having more than 2 cores.

Also MAKE SURE YOUR MOTHERBOARD IS COMPATIBLE with the CPU you want. You can't just pick one and put it in. :)

AMD will definitely make your dollar go farther with the CPU. Although I do not own the pairing atb85 mentions (FX-6300 and your 270X); on the surface it really does not look like a bottleneck will exist between those two components. Bottlenecks can occur when there is any slowing of transfer throughout your system though so there are no guarantees that you would not still encounter one even if the CPU and GPU work in perfect harmony. Sadly, no one can really tell whether or not you will endure one either. If there were they would be a god among geeks (and a millionaire to boot). There are just too many variables out there for anyone to tell your system will have one without running benchmarks. Ultimately, do not let that facet hold you back. If it happens it is not likely to be your CPU and GPU that are the culprits. So you look at identifying what is, and save to replace it when you can. Sure your performance will be hindered from what it could be, but if you are stepping up the CPU and GPU it is unlikely you will have equal or lesser performance than you currently are running with.

Thats not a sale.

Use this site for parts

rule no 1 never listen to a stupid nvidia fan boy

1- It's normally priced between 170-220$ so don't believe in Amazon's discounts.

2- It'll give you a SILVER Reward Code, not Gold one.

3- I just bought and installed R9 280 ( I installed it 2 minutes ago), it's AWESOME.You can find it for about 200$, buy it.280 is a lot better.

4- You can't find a better Nvidia product at that price, if your price range is about 100-250 go for AMD.GTX970 is better but more expensive.AMD cards perform better in BUDGET builds in almost every level but they're power hungry.Make sure that your PSU is enough for them, AMD cards need almost twice as power as Nvidia cards.

"I was about settled on it, but then I stumbled upon bottlenecking, and you see I'm on a 310 dollar budget for this year (around the same next year) . I plan to get both gpu and cpu this year, than the other parts next year."

So you're not going to be dropping it into an existing machine and it will be a brand new build that you can't put it together until next year? How far into next year will you have everything? If it's going to be a while into the year then you might as well wait until you have the money to buy everything at once. Prices might well come down in the meantime.