Your best bang-for-the buck (and still an awesomely good machine) will be an i5 CPU, base GPU, fusion drive (or 256 GB SSD), non-retina display purchased from Apple as a refurb. If buying the 21.5 inch rather than the 27, make sure you order the amount of RAM you want with the machine as it is not easily upgradable. For the application you describe, 8 GB might be enough.