ermm... split into two parts... 1 is to enjoy the night 1 is to commemorate the night/remember... so plan for a gift and a dinner...

budget split into 1/2 1/2... i dont fancy flowers so maybe ur gf might like flowers....

have a simple dinner, make sure not too heavy... light is fine... the gift must wrap properly...

doesnt have to spend $$$ a lot but must show sincerity ^^