There is no official ceiling on spending. Instead there is a general ceiling for revenues collected in electoral campaigns.
(2) The financing of the initiative groups and of the electoral campaigns of the electoral contestants by natural or legal persons shall be carried out in compliance with the following conditions:[…]
d) the general ceiling per country of the financial means that can be transferred to the “Electoral Fund” account of the electoral competitor constitutes 0.05% of the revenues provided in the state budget law for the respective year; the maximum ceiling for each constituency shall be determined by the Central Electoral Commission by multiplying the coefficient set by the Commission by the number of voters in that constituency; the coefficient is calculated by dividing the general ceiling of financial means by country by the total number of voters in the country;
Source: Art. 41(2), Electoral Code, 1997 (amended 2020)