Good question and I am investigating this also.
But I think the cost would depend on the complexity (setting up trusts? multi-page will, etc?) and the cost of living in your area.
I have no plans to set up a living trust. First of all, a revocable trust does not protect assets in some cases and an irrevocable trust may make it difficult if situations change. I plan to have it in my will that trusts are set up in certain circumstances (grandchild under a certain age) with instructions how the asset would be disbursed. But if the grandchild has already surpassed that age, then h=there is no expense to set up a trust.
Also, remember that not all places accept a POA. Even if you have given a (General, Medical, Financial) Power of Attorney to someone if you become incapacitated, not all places honor this - including the Social Security Administration.
They have their own form. So with your general/medical/financial Powers of Attorney forms, download these and have them ready in case they are needed (filled out and appropriately signed, of course). If any of the forms need to be notarized, you may find that this is a free service of a credit union or bank where you have an account.
It is also a good idea to re-sign these every ~ 5 years because the form may have changed since you last downloaded and signed it. You may also consider having not only a primary person for POA but a secondary in case the primary person cannot or will not accept the responsibility. Also check with your state/other entities you deal with (including your bank and insurance companies) to see if they also have their own POA.
Social Security Administration -
https://www.ssa.gov/forms/ssa-1696.pdf
Medicare -
https://www.medicare.gov/medicar.../publicforms/cms10106.pdf
Veterans Administration -
https://www.va.gov/find-forms/about-form-10-0137
Internal Revenue Service -
https://www.irs.gov/forms-pubs/about-form-2848
The Internal Revenue Service may accept a Power of Attorney other than form 2848 . However, for purposes of processing such documents onto the Centralized Authorization File, a completed form 2848 must be attached.