Hmm...As far as I know, "the" is never used after "there is/are".
This is the first time that "a group of girls" is mentioned. Noun phrases, mentioned for the first time, are modified by "a/an"."There was a group of girls following him".
After the word "girls" there goes the clarification "following him".
So, the question is, why is here used the article "a" instead of "the"?
In Paris, there is the Eiffel Tower, the Louvre, and the Cathedral of Notre Dame that are worth visiting.
In Paris, there are three sites that are worth visiting: the Eiffel Tower, the Louvre, and the Cathedral of Notre Dame.
This seems to say that you should consider the repair costs after buying the house, rather than considering them in your decision whether or not to buy. These are better in AE:If you buy the house, there is the cost of repairs to consider.
If you are thinking about buying the house, there are repair costs (that) you need to consider.
If you are thinking about buying the house, remember to consider repair costs.
If you buy the house, you will have repair costs.
Thanks, @PaulQ. This is a good example. In AE (or at least my dialect), where you say "there is", people say "one has" (or it's modern equivalent "you have")."If ..., there is the cost of repairs to consider." In BE, this is a common way to offer cautionary advice in advance.
In house buying, you have repair costs to consider.