Do you mean, that for companies 2, 4 and 5 the price is same for all following months?

Then in your table you must have last price for every month (i.e. for every row in table).

From this follows, what about companies 1 and 3? Did they have any prices for currently empty months (p.e. was price same as last one entered, until it was changed)? When yes, then you have to fill in table all rows for all companies, when those companies had some price.