What is she bred back to? How old is the cow? Is the heifer of show quality? Are they thf and phaf? Without seeing them its hard to say if its a good deal or not, so I will tell you this if you like them, think you have to have them, the price seems fair to you and you can spend that then get after it. If the heifer is show quality, she is eligible for Chi papers and I think Appendix Shorthorn papers (depending on if the cow was registered that way, could possibly still be just cost more money because of her age) then that would help justify the price. A good show heifer can bring that much and much much more by herself.
What I was getting at on comparing the 2 was if there is not a whole lot of difference between the 2 then go with the pair for only $500 more. I haven't had any trouble calving out my Heat Waves so far they have all calved out on their own.
$5K is way too much for a an average cow. Its very cheap for a good one - especially a three way. There are no guarantees you'll ever make your money back on paying that much for a cow. My only thought is that if she was really good, why is he wanting to sell her? Might be a valid reason, but I'd ask.
Another question to ask yourself, - if the cow drops dead tomorrow, will it cripple me financially? Don't put too many eggs in one basket. If you can afford to lose it, it might be worth the chance if she's good.
We sell a lot of three way heifer pairs for $2000-$2500 every year. Nobody would touch my best ones (top 5% of the herd) for that though, but we have a very long term view on those kinds of things though and we are understocked.