Have a question about ad pricing

One of my personal blog sites I run, someone contacted me and wanted to run an ad on the left side of my site. Its in the gaming niche. Gets about 300 page hits a day. Not really sure what I should charge them for this. Anyone have an idea? Never had someone ask for this before. I know people do it. Trying to get price idea.

Thanks,

PS, hope this is in the right section.