Late entry into the thread I know, but something I have been musing over.
The concept of a price for such a unit depends on a number of things. Fair value, "bid" price and "offer" price (in dealing terms) and of course availability... the ability of the unit to be sold at all.
There may be a value which one leasing company would be prepared to pay for a unit to another leasing company, which one would expect to be roughly in line with the lease revenue chargeable for that unit over its likely future life, plus or minus a bit. The future lifetime of the unit is determined by DfT policy.
However it would be wrong to say that these units have a price. They don't for a number of reasons; firstly the price is determined by what a vendor is willing to accept and what a buyer is willing to pay. But such a transaction has never been carried out; the 319s have been owned by Porterbrook ever since privatisation, there is no reference point (unless you include the bid of Porterbrook to buy the units from the government). Porterbrook would have an asset value associated with their assets of course, but this is a book value and not a selling price, they are different concepts.
The second reason it is wrong to allocate a price is that their destiny is already pre-determined by DfT and will be until they are no longer needed. The market is thus heavily regulated. Ultimately, they can't be sold onto the market other than to a small number of other RoSCos. A selling price may exist between rolling stock companies, but this is a unique and non-transferable value. If the question is, what would a 319 cost to anyone else who fancies exporting them to the North West, or Bulgaria, or the Isle of Man? There is no such cost price because they cannot be bought on the open market until they are surplus to requirements.
In essence, because the RoSCos would have to buy new vehicles, in order to replace the 319s, in order to sell the 319s (if that makes sense) you may as well set the price of a 319 at exactly the price of the brand new 377/5 (or even NXEMU) you would you need to replace that unit on Thameslink to fulfil contractual obligations! So roughly £4-6m a unit.
That's my (probably crooked!) view of the economics here.