There was no "Festival of Britain" Florin minted, you possibly refer to the "Festival of Britain" Crown (Five Shillings).
See "What is the value of a 1951 British Crown - Festival of Britain".
The last British Florin was minted in 1970.
The first British Florin was introduced in 1849.
There was no 1861 British Florin (Two Shillings) minted.
The last British general circulation Florin was minted in 1967.
The last New Zealand Florin was minted in 1965.
Austria ceased issuing Florin coins in 1867.
The last British Florin minted for general circulation was minted in 1967.
Such a coin does not exist. The first British Florin was introduced into circulation in 1849.
Such a coin does not exist. The Florin (Two Shillings) was first minted for general circulation in 1849.
There is no $ value (except as a collectors item), shillings are no longer legal tender in Britain. The Florin (Two Shillings), is part of an obsolete currency used by Britain and many of the 50 plus Commonwealth countries. At Britains conversion to decimal currency in 1971, the Florin converted to 10 New Pence. At that time, the 10 New Pence was the rough equivalent of $0.26 USD or $1.45 USD today.
Of the countries issuing a Florin (Two Shilling) coin, only Australia ever issued a commemorative Florin, but there were no commemorative Florins issued in 1936.
The first British Florin was issued in 1849, so it is unlikely that there would be a Half Florin coin minted any earlier. There was never a British coin called a Half Florin. If one existed, a Half Florin would be One Shilling.