Just updated the OP to reflect a few recent changes. Also, transfermarkt have got some values for transfer fees up, not sure how accurate they are but:
Holt - £2.64m
Vaughan - £765k
and inbound:
Olsson - £2.55m
Redmond - £2.02m
They reckon we've currently bought £13.5m worth of players for £14.7m, whilst £11.3m worth of players has left for £3.4m.
For comparison:
Swansea: £11.5m worth inbound for £8.1m spent, £3.5m worth departed for nothing
Stoke: £6.8m worth inbound for £3.1m, £3m worth departed for nothing
Sunderland: £15m inbound for £12.5m, £12.7m worth leaving for £11.3m - basically broken even so far surprisingly
WBA: £440k worth in for nothing, lost £5.1m worth for nothing
Everton: £11m worth in for £9.7m, £2.3m departing for nothing
Southampton: £7m worth arriving for £8.8m, £1m worth leaving for nothing
Villa: £15.1m worth in for £10.8m, £11.6m worth leaving for £2.6m
Hull: £14m worth in for £5.9m, £4.4m worth leaving for nothing
Palace: £3.7m worth in for £5.5m, £2m worth leaving
Cardiff: £4m worth in for £7.7m, £700k worth leaving
Not sure how helpful those stats are, as in terms of gains, we've currently spent £11.3m in increasing the value of our squad by £3.4m


But the most canny clubs so far have perhaps been Swansea, Stoke, Sunderland, Villa, Everton and Hull, whilst ourselves and Southampton have done sightly worse, with Cardiff and Palace paying over the odds the most.