Did you just pull that number out of the air?
The only reason I ask is because when I looked at the item, I was thinking (out of the blue) that 10,000 to 20,000 might be more suitable.
I was going by about how many wands of lesser vigor would last you for life.
Assume 13.3 encounters/level. Assume you need to heal, on average, 80 hp/encounter. The game lasts 20 levels.
You'll need to heal 13.3*80*20 hp.
A wand of lesser vigor heals 11*50 hp, and costs 750 gp.
750 *(13.3*80*20)/(11*50) = 29018.19 gp
Now, healing with the ring of regeneration is much slower than using wands. That means it should be discounted compared to our bucket o' wands. Furthermore, you can't just pass the ring around and heal other party members. It also takes up a slot. That would put it down to half price, say, around 15000.
On the other hand, there's the wild card of how much regeneration is actually worth (in addition to the healing). I suppose a particularly badass dude might cut off their own finger to activate the "regenerate (as the spell)" to cure " 4d8 points of damage +1 point per caster level (maximum +35), rid the subject of exhaustion and/or fatigue, and eliminate all nonlethal damage the subject has taken."
I'd add about 5k for that ability, since it doesn't do much to enhance the preexisting hp regeneration.
That brings us to 20k, which is cheaper than the bucket o' wands, but the wands don't take up a slot and can be shared with other PCs.