It depends on the size of the vehicle that you're renting but, unless it's a larger car or some type of specialty car, that's seems high to me. However, most good rates will become available much closer to the pick up date.
When we reserve a rental five or six months out we generally do it to make sure that we'll have the vehicle size that we want. Then we start looking at rates a month or so from the rental date and modify our reservation to take advantage of updated, lower base rates and/or coupons that can be added to the reservation. The cost difference can be substantial.
If you haven't already looked at the car rental section at mousesavers.com, I'd suggest that you do that as they often have several discount coupons available for each of the car rental companies.
Dick Taylor