Reseller price should be waaaaaaaaaaay lower. The reseller has to shoulder the burden of renewal fees and the fact that he may never sell the domain for a profit. I think reseller prices should be about 10-20% of end user prices (though like Brad said these are unknown and have to be estimated). This is just a mental exercise though...there are so many factors that influence price.
Let's say for example that I had a domain that I thought an end user would pay $1500 for. Let's say it was a triple premium lll.co (these seem to sell in that range). The reseller market for lll.co is probably up to $150 or maybe a bit more (for top triple premium). That can be a guide but it's hardly scientific. Sometimes you can't even sell an lll.co to an end user for more than a couple hundred. :D
I will add that this is mostly for .co where the prices are highly speculative and most domains were purchased for reg. fee. I think the spread would be a lot tighter in .com where the value is more established.
You would be doing very well to get a reseller to pay 3/4 of its maximum potential end user value.
As Brad mentioned it's very difficult to assign a specific value of a domain to an end user. It's worth what they're willing to pay, which can be hard to determine. I see a lot of high sales that make me scratch my head a little, but when it comes down to it, for many companies $10,000 or $100,000 is "a drop in the bucket" if it's something they want.
It's hard to make good money selling to resellers. I frequently find that end users are more than happy to spend a couple hundred bucks (or more) for domains that might not sell for $5 or $10 here.
Brad is right. It's hard to establish an end-user price. But assuming you can do so, as a domainer, I probably wouldn't pay more than 10% of that end-user price. I think the 90% discount to reseller pricing is about right, imho. The buyer is assuming all the risks of making a sale to an end-user, hopefully sometime in the future.
I tend to agree with the 10% to 20% value of the assessed end user average price. Also, as others have mentioned, value (just like beauty) is in the eyes of the beholder and this will vary greatly from one prospect to the next. There's just way to many factors at play to narrow down an exact price without missing a few variables that could potentially decrease or increase value that you may have over looked. At the end of the day, a domain is truly only worth what a buyer is willing to pay for it or what a seller is able to convince a buyer it's worth. Whether you cater to resellers (quick flip for low profits and less risk) or end users (Higher profit long hold selling assuming all the renewal and loss risks) a good presentation is essential in either business model to maximize your ROI.