The budgets of German parties for the ongoing federal election campaign are relatively modest; according to SpOn a few weeks ago;
SPD ~23 million €
(remaining right wing of former social democrats)
CDU ~20 million €
(conservative almost_no_reforms politicians)
Grüne ~ 5.5 million €
(greens, previously claimed to be pacifists and against militarised foreign policy, then went to war ASAP in '99 and fell in love with ISAF. They also claim to be civil liberties lovers, but this seems to migrant and women topics only)
Die Linke ~4.5 million €
(former West and East German communists plus former left wing of social democrats)
FDP ~ 4 million €
(self-proclaimed liberals; pro-employer and pro-rich party)
Piraten ~ 0.4 million €
(young, information technology-affine party; concerned about surveillance, internet neutrality and copyright topics)
The CSU (Bavarian substitute for CDU, more right wing and used to governing Bavaria) spends 9.5 million €, but that's at the same time a state-level election campaign.
These sums are for all federal parliament districts, as the whole parliament (Bundestag) is up for election. It elects the Chancellor and thus indirectly his ministers - they are not up for a separate vote. Germany has a population of more than 80 million.
The budgets are very small compared to the importance of the election. It's true that parties dodge some donation restrictions by outsourcing much work to staffs of party-aligned political foundations which are not restricted the same way, but these do not intervene noticeably in election campaigns.
I think we can conclude that big money does not buy our government; whatever influence it has is more likely rooted in much more subtle means of influence (socialising, respect, power over information, 'helping' with drafting bills etc.).