england-and-wales
Assuming the estate is solvent, then reasonable funeral expenses are allowed "according to the deceased's condition in life". There is no rule of law which specifies exactly what is allowed and what is not - it is for the judge as the trier of fact (if the matter should come to court for any reason) to decide in the individual case.
Williams, Mortimer and Sunnucks (22nd Edition) comments that:
38-15 The question is one of fact. Thus, the cost of a tombstone was
allowed... in one
case but not in another. The cost of mourning was allowed in one case
but not in another. The cost of reinterment in order to fulfil the
last wishes of the deceased has been allowed in Canada. A payment of
£93 odd for mourning rings distributed among relations and friends of
the deceased was allowed by Lord Eldon where the will gave no
directions, but committed “anything not specified” to the discretion
of the executors. In a case decided in 1691 the sum of £600 was
allowed on the funeral in his own country of a wealthy local
celebrity.
Regarding the last case, the case report from 1691 states:
There had been £600 laid out in Mr. Offley's funeral, which the court
decreed should be a debt to effect the trust estate, Mr. Offley being
a man of a great estate and reputation in his country, and being
buried there ; but if he had been buried elsewhere, it seemed his
funeral might have been more private, and the court would not have
allowed so much.
£600 in 1691 would be worth approximately £130,000 today but he was a man of great estate and reputation in is own country, we are told.