Greetings.
It is difficult to put an accurate value on medals because much depends on the rank or fame of the person to whom they were issued and whether or not that person was killed in a famous action (for example a medal trio for a soldier killed on the first day of the battle of the Somme, or a seaman killed at the battle of Jutland, or an airman shot down by Baron von Richthofen). Medals for Sir W F Miller would, because of the knighthood, be rarer and more valuable than the same medals issued to Corporal Miller. Sets of medals issued to one person are worth more than the combined value of single medals. Original cases also add value. Rarity (of either the medal, the clasp, the set, or the regiment) is also a factor.
To get an idea of medal values I suggest you look at a specialist website (such as
http://www.british-medals.co.uk/ or
http://www.liverpoolmedals.com/) and an online auction site (such as e-bay).
Very approximately the lowest values are:
Indian mutiny medal (with no clasps) £200
British South Africa Company medal (with no clasps) £450
Queen's South Africa medal (with no clasps) £90
Cape of Good Hope general service medal (with no clasps) £150
1914-15 Star £30
British war medal £18
Victory medal £18
British war medal and Victory medal pair £45
British WW1 medal trio £100
US ribbon pair on bar £5
Bear in mind that these are the lowest values and that the value could be multiplied by 2 or more times depending on historical interest.
Personally, I do hope that the medals remain in the family (I was very upset when I learned that my Dad had pawned his medals so they are lost to the family!), but if they must be sold their value would be increased by having documents to go with them (service records, obituaries, photographs etc.)
All the best
Philip