It depends on whether I'm currently playing and what the offering is.
First up, if they did digital versions of the Dragon and Dungeon magazines of old (not the 4e successor, which was something of a step down, and not Dragon+), then I'd subscribe in a moment. And that whether I'm playing or not - but it would need to be in PDF format or similar.
For anything else, I'd only consider it if I'm actively playing. And since my games at the moment are in an environment where online access is difficult, it would either need to be PDFs or tools for preparing the game. I have no use at all for D&D Beyond, a VTT, or anything like that - I can't use them. But, I'd happily pay for really good tools for preparing a game... provided I'm actually playing.
In terms of price, $25 a month is probably my limit.