Sally, if you were to ask a French electrician, he - or she - would probably try to convince you that you better renovate the whole electrical installation to the regs of today, including a wired network for phone and data. Not conforming, what's in a name, many shades of grey. It could be dangerous, or just not conforming to only some non essential regs. You can fly in an electrician for a second opinion. Must faster: consider this report as a bargaining chip to get the price down. Rule of thumb, depends of course on surface and quality of the existing wiring and contents of the distribution board, earthing arrangements etc: set apart a budget between 2K and 7K for a (partial) rewiring. To make an existing installation safe doesn't imply that you have to live up in detail to everything that has been laid down in the French electrical code, NF C 15-100. Skipping the communication network will not harm anyone. Food for thought: the French president Hollande promised us (May last year) a simplification of construction regs, including the electrical code. So what is obligatory today might perhaps melt away as snow in the sunshine of spring 2016. I must admit: this belongs to the department wishing & hoping. See also this topic.
But having signed the compromis de vente already my comments are a bit too late to lower the asking price I'm afraid. Might be useful however to do a selective rewiring.