The discretize function will do most of the job. You may have to play around with it a bit, but something like this should work:
bins = 43.5:1:60.5; % define some bins that cover the range of interest
assignments = discretize(Prices,bins); % get a vector telling you which bin each price is in
% compute how much was sold in each bin
bintotals = zeros(size(bins));
for ibin=1:numel(bins)
bintotals(ibin) = sum(SoldElectricity(assignments==ibin));
end
binprobs = bintotals / sum(bintotals); % compute the proportion of the total in each bin
plot(bins,binprobs);
