Ok OP you got some good info here, I realise you are not familiar with foreign punting, or you wouldn't of said punting in Germany will be expensive, yes wages and the cost of living in Deutschland is high, but it doesn't always mean whore prices are high too. And I've remarked in the past that some hookers in Prague are more expensive than Germany, It's not 1992 any longer, prices have risen in Eastern Europe, especially near the tourist areas.
I can be the king of cheap, so you come to the right place, you want to go for a weekend, cheap hotel with a few cheap punts, ok and your total daily budget? £100 hotel for two nights, that's not budget, I paid about 30e a night for a room in Berlin, there is plenty of choice.
Berlin would be a good punting option, there is no laufhaus/eros centre type RLD in Berlin, but street girls are found down Kurfuerstenstrasse, Airport girls great value at 60e for 5 hours, Anni Porshe a option. Artemis isn't budget, 80e entry, then 60e for a session, can add up, but you could spend all day there, food and drink included, lots of stunning naked girls.
Other cities to consider, if you're flying from London, Cologne, Duesseldorf, Frankfurt are worth considering, for Vfm Partytreffs similar to Airport girls will be best value, several of these can be found in the Dusesseldorf area.