normally 3* worth around 30-50k and for 4* the price is around 150-450 depend on units.
Samantha and Paige is event exclusive so after event you may sell her at 250k and more.
(All price I said is based on lv1 tho)
for 5* the cheapest is Fiona, price is around 10TE (time elixir) or less but she is awful and worst than some 4*.
The other REAL 5* you maybe use 4-5 max 4* to trade for, but most 5* sell in form of TE.
50k=1TE but in event 70-100k =1TE
Hope it help and welcome to the forum