OP is landing 22 00 pm so traffic will be over.
In case one doesn't not have a change for Taxi/ train there are tons of 7/24 open exchange booths where 20-30 GBP/ EUR/ USD/ you name it / can be exchanged to fund our trip do the city.
Rates are worse than on the streets but not dramatically so and on such small amount one will not lose that much, perhaps 10-12 % . Also rates are uniform throughout the airport so no need to hunt for the best.
Of course exchange booths at airport train station are offering close to best rates everywhere ( in October last year I got the positively best rate for my currency there , better than anywhere in BKK and PTT ) but they close before midnight so for late comers are of no use unless somebody is thrifty type who wants to camp there till morning to obtain such good rate, LOL