Regeneration potions are a repackaged way to sell ghast tears which go for 60r each. One tear makes three potions. Adding in additional costs (glass, nether wart, redstone or glowstone, sulphur, labor) and a fair price would be 40-45r when you are sourcing your own ingredients.
Bit cheap. If you factor in the labour like you say you have to a) have a computer able to render the nether with a safe FPS b) have the gear and survival skills to survive in the nether and c) have the luck and ability to collect the tears. Since most people don't do this that is what jacks the prices up.
