The Steam Machine is nothing special either and it’s being sold at a ridiculously price. I wouldn’t hold my breath on the Frame being affordable by any stretch of the imagination.
I think it’ll sell well though because of the form factor, Steam OS simplicity (and the size of many people’s Steam libraries), and the fact there are not actually many options with the living room friendly form factor and someway reasonable modern gaming performance.
The Frame on the other hand has no competition. I know I’m buying one. I hope it’s more reasonable but it could be a worse deal than a Steam Machine and… yeah.