Use ITA to check taxes:
matrix.itasoftware.com
Now I have some possibly good news for you. If Iberia.com is quoting you 4,500 Avios + €36.58 cash, then it looks like you have not earned any Avios in your IB+ account in the last 12 months.
I say that because if you had, your account would be quoting you this flight as a 'Reward Flight Saver'.
RFS are available on shorthaul flights in each of the three Avios currency using schemes, providing you have earned an Avios point in the last 12 months in the scheme you want to book from.
And Vueling are only an IB+ partner, so can only be booked from IB+ accounts.
With RFS, the taxes, charges and surcharges are replaced with a flat fee to the airline (the flat fee varies with distance band, but not with the taxes on the specific route), and it is cheaper than them (usually significantly cheaper).
If you earn 1 Avios point or more in your IB+ account, say credit a flight, or hotel stay, or transfer some Amex Membership Rewards points, etc. then your trip price would reduce to:
4,500 Avios + €17 .50 TOTAL - that flat fee of €17.50 is in the place of the taxes, charges and surchages, which are paid by the airline.
a BAEC HHA is a wapper for a collection of individual BAEC accounts that make up the HHA. Each member of the HHA has their own balance. The HHA total is just them all added together.
a BAEC HHA lets people pool their Avios to spend from a combined big total balance - but spend from BAEC. The miles never go into a single pot.
There are three schemes which use the Avios points currency, BAEC, IB+ and what used to be called Airmiles.co.uk - now confusingly called Avios.com (a mass market shopping earning scheme in the UK market only).
Now, each of these schemes allow people to move any of their Avios freely between their accounts in each of the schemes using 'Combine my Avios' (CMA)- which you can find when logged into any of the three schemes.
However there are the following restrictions with IB+:
- IB+ accounts need to be 3 months old before you can use CMA with them at all
- IB+ accounts need to be active (have earnt an Avios point) before you can use CMA with them at all
- IB+ accounts can NOT use CMA with BAEC accounts where the BAEC account is part of a BAEC HHA.
There is a work around to the last bit. If your BAEC account is part of a HHA, you can still transfer from BAEC to Avios.com. And from Avios.com to IB+.
However do note: You will only be able to transfer from your personal pot at BAEC. Not the combined HHA balance.
Also, your account will still need to satisfy the first two, before you can transfer in.
Hope that makes sense.