Higher level casters don't sell themselves short. Once the 1st level cleric is out, the 5th level cleric does not drop his price. Since higher level PCs have deep reserves of life force, 3 gp-5gp per HP sounds fair accounting for the risk involved with a temples clerics having their spell stacks drained to heal someone.
There's nothing wrong with a 3 to 5 gp cost, except that there's no reason to pay it; it's cheaper to heal from wands oneself. High level casters may charge more than low level casters, but if they price themselves out of the market, they make no money at all. No-one will pay 100 gp for a CLW from a 10th level caster, so why would he charge that? Remember, using the PHB services spellcasting prices for healing requires discretion anyway, since as written, you need to make the request 24 hours in advance.
Even if you don't have anyone who can activate a wand of CLW (no cleric, druid, ranger, or paladin, and nobody with UMD), you can still own one, go to the cleric, and have him activate it when he is out of spells. This probably costs a little extra, but since he isn't expending any resources, it can't be that much.
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gnfnrf