A lot of sites are recommending buying thebiggest drive you can afford.
With the exception of a few recent hot deals, you generally pay MORE per GB with a bigger drive. Like everything else in this industry, linear gains cost exponentially more.
The reason enthusiast sites suggest going with larger drives is more the increased performance benefit of interleaving more NAND channels to the controller, more so than capacity or cost.
More NAND = more performance up until the point where the controllers channels are saturated and it starts costing performance with larger lookup tables, etc. while no longer adding channels to compensate.
Right now 256GB drives are the sweet spot dominating performance scores. 128GB models fall to the left of the bell curve and the 512GB models fall to the right of the bell curve. 128GB don't have enough NAND to make the controller work hard, and 512GB have double the NAND to search through while being limited to the same number of channels (why 512GB based models see IOPS nose dive off a cliff compared to 240 GB versions of the same model)
When new generation controllers have more channels, faster processors, more cores, and bigger logical to physical look up table caches to deal with 512+GB effectively and efficiently (and a new interface faster than SATA 6G emerges), we will start seeing easy 1000+ MB/sec 180,000 IOPS 512 GB SSDs.