It turns out the internet is a fascinating place for people looking for information on food prices. The Food and Agricultural Organization (FAO) has some great price tracking tools here that allow you to make your own charts out of different commodities.
I have pasted several different charts below to give you an idea of food price developments in the Congo and their possible political importance. In the first chart, I compare cassava flour - probably the most important, cheapest staple in much of the country - in Kinshasa, Kisangani, Bunia and Lubumbashi. Two observations: Kinshasa is much more susceptible to fluctuations in the food markets, even the local one (all cassava flour is sourced locally), due to its reliance on the hinterlands for food. So an increase in fuel prices and bottlenecks in supply will affect this behemoth of a city much more than places like Bunia, where there is plentiful local production.
My second observation on this chart is that, while cassava prices have risen gradually, increasing by 15-35%, they are still below their crazy peak in 2008-2009 during the financial crisis. (We also need to be a bit careful about this price index, as it is expressed in Congolese francs, which have seen 10-20% inflation over the past two years - some of the economy is still dollarized, which provides a bit of a buffer to inflation in local francs).
On the second chart I compare different commodities in the capital Kinshasa - the reason for this focus is that, if there is going to be serious urban unrest, Kinshasa - the third largest city on the continent - is a likely candidate. Wheat - which is all imported - is obviously more susceptible to fluctuations in international markets, but otherwise most commodities seem to be more or less tracking levels of inflation in the country (I'd have to do a more rigorous analysis of the prices to be sure of this) and (possibly) fuel prices.
The last chart is a comparison of two African countries that have seen urban unrest linked to high food prices recently: Uganda and Burkina Faso. Here, the prices of imports (not the locally produced sorghum in the case of BF) has risen much more steeply than in the Congo, by 60-150% over the past year (I'm eyeballing it).