Anyone know where to get a decent price on a rope?

I get my ropes from REI. Wait for a sale or use your patronage dividend to save a bit. Rope used for climbing or rapping is not a good thing to go cheap on.

I've had a number of friends pick up ropes at justropes.com

As hikermor said REI is also very good if you wait for a sale.
I also buy a lot of climbing gear at Eastern Mountain Sports when the run sales.
Both REI & EMS will match each others prices.

Standard disclaimer.

I'm treating my response as you know what you're doing and what you're looking for. For anyone reading who does not climb..nobody should be buying ropes and trying this without proper training unless you're idea of fun is to be broken or dead.

what's wrong with the ropes at Harbor Freight?

Those are perfectly fine ropes for their intended purpose. I just checked their website, and everything in their inventory was polypropylene or sisal of fairly small diameter. Natural fibers like sisal have long disappeared from climbers' gear, replaced by materials like nylon which are stronger, more resistant to deterioration. When made up into line for climbing and other life support applications, the fibers are woven up in fairly sophisticated techniques that enhance the handling ability of the rope, as well as its wear resistance and durability.

You can even obtain rope designed specifically for rappelling; it is quite stiff, with far less stretch than nylon - a desirable characteristic when undertaking very long rappels of more than 200 feet or so. These are the best for cave exploration and rescue applications. In "normal", rappelling, where lengths of 100 to 150 feet are most common, the more elastic nylon ropes work quite well.

Yes,they are expensive; geezer that I am, I can remember when a perfectly fine climbing rope could be had for all of twenty dollars. Today you will easily put down ten times that amount, but you get equipment that is stronger, more durable, and better in every way for its specialized purpose. When you are dangling above the bottomless pit, I am sure you will agree that you are worth that additional cost.

If the rope will be FOR RAPPELLING ONLY, you might be able to get a serviceable one used from a conscienscious and reliable seller, FOR RAPPELLING ONLY. A rope retired from climbing use may still be in fine shape FOR RAPPELLING ONLY. I hope you caught my emphasis above. You would have to trust the person selling you a used rope to be honest about this history of falls it has taken, how it has been treated, etc.

Your logic is impeccable, but the devil is in the details and the conditions you establish. Even a conscientious seller may not realize how much damaged and degraded a rope might be - the only way I know to establish the strength of a used rope involves destructive testing. You also have another problem. You may designate a rope for rappel only, but situations will arise where you will be tempted or impelled to use it for leading or belaying. You might get away with that for a while (and you likely will), but sooner or later.....

The only rope worth loading onto your pack is one that is capable of full service. Once it is no longer serviceable for leading, only non climbing, non critical applications are appropriate.

I have to chuckle at my resolutely conservative philosophy here, especially when you realize that the first rope I ever used (incorrectly, I might add) was a 5/8" manila line that I later learned had come from a spool condemned by the telephone company. Since then I have witnessed entirely too many bad situations involving junk ropes. Cut corners and save money somewhere else.

I like to have a second rope used as a belay backup to a rappel rope when ever possible. Even with experienced users.

If you have the knowledge and experience, a dedicated rappel rope can be of the
static variety, which can save money and often will wear and perform better at it's
task than a dynamic climbing rope.

Examples.

http://www.amazon.com/Edelweiss-Static-Rope-11mm/dp/B0045E5U8O

http://www.greatoutdoorsdepot.com/edelweiss-low-stretch-static-rope.html

If you are in any situation that might include a fall, a dynamic rope is critical
however.

I've gotten too old to climb anymore, but my daughter is heavily (HEAVILY!) into it. Being the poor college student, she is of course short on funds to buy things like a replacement rope (her original one needed to be retired). And dad's can't let their little girls climb on less-than-perfect equipment.

I bought her the rope below based on what she told me her requirements were, and the recommendation of the REI salesman:

http://www.rei.com/product/831016/edelrid-eagle-pro-98mm-x-70m-dry-rope

I paid the originally listed price on it. I see it's for sale much cheaper now. FWIW, my daughter says I chose well, and this is a nice rope for her climbing style/requirements/whatever.

She calls it "the green mamba".

You are a good Daddy! Lucky girl....