You may want to keep an eye out on the classifieds for them, as they go for around $90 - $110 usually these days. I don't mind that they don't have detachable cables because the stock cable is probably the best I've seen on an IEM yet. The GR07 is a bit more resolving in the treble, so it's a bit brighter and is prone to some slight sibilance (it's a bit more peaky around 10khz) but after some usage and break-in it smooths out a bit. Sony Hybrids work best on the GR07, the nozzle is too narrow for the RE-400 and it will have an effect on the treble mostly, making it darker/bassier and altering the tone a hair. The RE-400 is less fatiguing overall, but both can be and it is dependent on listening volume mostly because both are fairly neutral. On my RE-400 I use some Meelectronics single flange tips currently (wide nozzle, same diameter as the filter basically) or the 'hybrid double flange' type tips:
http://head-direct.com/images/product_images/2013-08-12/b8d533cd917e7371743c8f7de32225ca/00-58-37742-4ac1e3f4b94d81d82cea42ebf448a29e.jpg (bottom pair, also wide nozzle opening)
Both are very good, equals I would say in most regards. Definitely enjoy the mids and slightly softer treble of the RE-400 most, but the bass and speed of the GR07 are nice as well...each has it's purpose in my collection.