Start off by calling up or visiting the
Hamburger Tierschutzverein.
If they don't have any dogs you like, move on to the
Franziskus Tierheim (Bund Gegen Missbrauch der Tier)
If there's still nothing, then try
ABC TierschutzAlso scan the local little newspapers for folks who might be looking to rehome their dog for various reasons.
Then there are all the organizations that help dogs outside of Germany. We got one of our dogs through
Tierhilfe Antalya. Unfortunately they are currently revamping their web site so there isn't a lot to see there.
I've never really calculated my monthly cost for our two terriers, but it easily adds up. Food, treats, collars and equipment, training & transportation, vet fees and medicines/tick treatments, doggie haircuts at the salon, etc. Oh, and mustn't forget the chewed and damaged pillows, blankets, flower beds, and bras (long story

)
Good luck!