From St. Petersburg To Germany For 38 Euro
First Step: St. Petersburg to the Latvian Border
Go to Baltiski Voksal. There are frequent suburban trains to Luga, a town around 100 km south-east of St. Petersburg. It costs you 60 roubles. I had a bicycle with me, so they charged me additional RR 4,00. The trip to Luga takes around 2 and a half hours.
In Luga you queue for a ticket to Pskov. This takes you not much longer than 10 minutes. There are 3 or 4 daily trains to Pskov. The fare is 56 Roubles and takes some 2 hours.
In Pskov there are different possibilities to come to Latvia. You can go there by bus, or - as I did - by train to the Russian-Latvian border (33 Roubles; the town is called Pytalovo) and then by bicycle across the border. I did the 40 km at night which I do nit really recommend, as there is no street light at all. But if you like adventures and are not scared of real darkness and silence, this might be a good experience. You may realize trucks coming from the borders already five minutes before they pass you by, as there light is reflecting in the clouds.
For those who don't have a bicycle, the easiest way to cross the border is to take a bus from Luga to Rezekne (5,00 Ls).
Second Step: Latvian Border to Daugavpils
13 km behind the Latvian Border there is the city of Karsava where I hoped to find a train to Rezekne. Unfortunately the station is not maintained anymore. So I slept on the old platform - where the grass has grown already to a height of one feet - and found in the morning - located in the center of the town - a bus station. There are frequent busses to Rezekne for 0,80 Ls and I could pay them, as there is an ATM near the station where I was able to draw money.
In Rezekne I entered a bus and went to Daugavpils for 1,60 Ls. The driver wanted 0,40 Ls for the bicylce (I still don't know, if this was the official price or bribery. I have no receipt but it somehow seemed offical to me.).
Third Step: Daugavpils to Warsaw and then further to Germany
I had much luck to be in Daugavpils on Monday as this is the only day to catch a bus to Warsaw (Poland) for 11 Ls. I took this bus in the evening. If you are there another day you probably will find other possibilities to continue your travel. The most important thing is that you are flexibile and don't make your plans for hours to far in advance.
Warsaw is the place where you can buy a train ticket to Germany. I bought a ticket to the town closest to the border (Zgorcelec / Görlitz) if you have happen to need to get to Dresden. The prices vary depending on the speed and luxury of the train. The first ticket I wanted to buy was for 83 Zloty (+11 Zloty for the bike). I had not that much Polish money, so I looked for another train and found one for 48 Zlotys.
The whole trip took me two and a half days. You can make it probably for less money if you have more time or faster (if you spend more money). A problem is that most foreigners need an extra transit visa for Belorussia. So even if you want to go from Moscow to Central Europe you have to go via the Baltics.
I also heard of the possibility to take a ferry from St. Petersburg to Kaliningrad. This is an inner-Russian ferry line, so there should be no problems with your Russian visa. However, don't take this for granted as laws are changing every week and every customs official is different.