Analog has given us a nice write-up of the low-end Grados alongside the RS1 in his thread: And The Winner: Grado 325is Review (and Compared w/60i, 225i, RS-1)
I have been looking at cans at different price points within my budget. I originally was looking at circa $150, but ended up going for a pair of 325is from a dealer who was selling their demo pair for a strong discount.
This go-round, I listened to the RS-1, the 325is, the 225i and the 60i. All listened through the headphone out of the McIntosh C2300 with the Bel Canto CD player as the source.
Moving down to the 325is, you give up some depth of soundstage, some dynamic slam and some relaxation in the top end (and get perhaps a hair less smoothness in the top end.). Still, this is probably the first level of a complete, real high end headphone offered by Grado to my ears.
Going down to the 225i, you still get a musically communicative headphone, but the highs are significantly rolled off headphone. The midrange is not nearly as detailed, sounding rather gray in comparison. When listening to acoustic instruments, you don't nearly get the sense that you're listening to real instruments the way you do with the higher priced Grados. Still, they communicate music well and you could do worse. They certainly aren't boring (unlike some other lower priced headphones I have listened to).
The 60i headphones are a great value but, in an absolute sense, are opaque, rolled off and grainy. I still think they make more interesting music than anything else in its price range. I also recommend replacing the closed foam ear pads with open ones, especially if you are a classical music listener.