What are the costs associated with carrying lots of genetic material
It is generally known that the smaller (or less complex) an organism is, the more "condensed" it's genome is. For example, bacteria (or some eukaryotes) have operons (http://en.wikipedia.org/wiki/Operon) or overlapping genes using different and they don't have introns, which alltogether saves a lot of space. 

There are many reasons for that. Available space in the cell is definitely not one if it, however. Energy for copying and maintenance is a good point, but you have to keep in mind how evolution works. Bacteria and unicellular eukaryotes are usually adapted to a very specific environment in which they can reproduce rapidly. This means, they only need a small set of genes, specific for this environment and they have to reproduce very frequent, which means they are very prone to mistakes during DNA-copying. Such a mistake can lead to the death of the cell, which in this case equals the death of the organism.

In higher organisms however, the advantages of a bigger genome outweigh the disadvantages by far. Evolution can happen much faster because and mistake while copying does not necessarily lead to the death of the whole organism. Adaptation to a much greater variety of conditions is also necessary, e.g. when you look at plants: Their genomes are (on avarage) much bigger than the ones we mammals have, because they cannot move if the conditions around them become unpleasent. Instead, they need to find a way to adapt. This means, a big genome is in this case a fitness bonus. More interestingly, plant genoms are highly mutable (http://en.wikipedia.org/wiki/Transposable_element), which was originally thought to be a huge disadvantage.