Hate to say it, but considering what your baseline plan was... its about in the ballpark.
I ran a sanity check through one of the national rental car sites, and got around $800 for a convertible for that period of time (departing and returning to Las Vegas). $700 looked about right for the plane tickets.
My experience with hotel rooms run around $70-90 as being a reasonable room cost (AAA 2- or 3-diamond places, but not 4 star hotels, etc), plus another $10 a night taxes and fees etc. A good meal in a family-style restaurant will be around $30 or so -- a fancy meal (somewhere with a wine list) would be around $40-50. So $150 a day for traveling expenses (no gas) is reasonable, but may be on the low side if you want to go higher end ...
But if you look at your costs, your highest costs are a) Lodging b) Car, c) Food & Misc, d) Air Fare, and e) Gas.
For lodging, as Judy has suggested, you might consider doing a bit of camping to save money while traveling. That would knock off costs by around $50 a day you campe. Although, this is your honeymoon and I fully expect you'll be spending a day or two somewhere very nice enjoying room service and not doing a lot of going out. But once you start traveling, even staying in a campground every few days, you can save substantial money. I'll typically stay in a campground for 1-2 nights while traveling, and then get a reasonable motel room for variety. Staying in a campground for say 6 nights would save you around $300 or more. 12 nights would save you $600, essentially near the cost of the plane tickets. Judy suggests you can get a basic reasonable set of camping equipment for 2 for around $100. That's possible -- but my estimate is it will run around $170 or so ($40 for a tent, $30 for 2 sleeping pads, $60 for sleeping bags for 2 that zip together, cooking equipment $20, ice chest $10, and 2 camp chairs $10 -- you can get these cheaper perhaps, or quite a bit more expensively, and it can be reused on future trips)
If the convertible is required.. then it may not be negotiable. But dropping back to (for example) a full-size SUV would cut the cost around $150, and to a full size sedan would drop it around $400.
Food costs can be minimized by a) taking advantage of any hotel/motel free "continental breakfast", b) picnicing a lunch out of the cooler on the trip, and c) doing an occasional cooked in camp dinner if you're camping. You'll need a cooler/ ice chest of course, and have to hit up a grocery store for bread, sandwich meats, fruit, etc. but its usually not a problem and sometimes really nice to just find a lonely spot and have an intimate lunch for two. I'll also note, that you can toss in a reasonably good bottle of wine and a corkscrew for well less than restaurant prices (like 1/2 to 1/3...) and if you're camping enjoy a glass of wine, watch the sun go down and enjoy each other's company.
