What if entry cost is variable?

Usually cost of entry is considered as a fixed cost; however, if we assume a lathe could be split into several smaller parts, and each involves different levels of entry costs. The firms do not only consider whether they enter the market or not, they also need to decide which sector or sectors of the ,Arlen they want to enter. Low entry cost means higher competition, as more companies are likely to be qualified to enter these sectors. However, entering the sectors with higher entry costs does not mean they can gain monopolistic power or oligopolistic power, since they are likely to face some degree of competitions from other sectors. Moreover, if the bar is high enough to stop all but one firm from entering the sector, then there is some degree of competition within the sector as well.
Under such circumstance, firms have to consider the cost and benefit from entering each sector by considering the factors within the sectors and factors across sectors. Once we consider all good and service markets as a whole market, and each individual good or service market is a small sector of the entire market, this means businesses have to consider the entry cost for its target sector but also its target relation with all other sectors.