I’m going to have a class probably around the beginning of next year (See Gauging Interest - RepRap 3D Printer Build Class V2) building the Makerfarm Pegasus which seems to be a nice $400 kit. It comes with a E3D lite6 hotend which is a good starting point (won’t go over 240C so no nylon or high temp materials, but you can upgrade to a E3D v6 for $80), The rest of the kit looks decent, you could replace the lasercut and printed parts easily, the extruded frame seems like it could be rigid or made rigid with struts.
I would mainly avoid all the chinese-based i3 kits mentioned above because of the service or lack of service you will get. Folgertech is supposedly OK, but you will be replacing parts as Frank mentioned to get it to print well. Makerfarm has an actual guy Colin that provides support
Printrbot Metal is my choice as well but it’s a little over $400 for a Simple kit, you’ll still need to build an enclosure and heated bed, all-metal extruder upgrade.