Is there a site you can reliably do this?

Nope

this was back in the days a small guideline for me

https://tools.harrogath.com/valuecalc.html

It depends on what u looking for and what realm i guess but i can give u some examples,

ring could roll 6 stats for example hdin would want:

10fcr
25str
15dex
20life
11@

same goes for amulet:

2pala
20fcr
30str
60life
xx mana
xx mana reg

Make price check threads in your trade forum and wait until you get several answers, many may give fake low prices to try to coup it off you.