You really need to go through the pile and see what's in there. If most of them are absolute junkers and BSO's with some missing saddles, a wheel, a crankset etc, then I'd agree they are probably close to scrap metal value by weight. However, if there's a reasonable number of viable bikes in there, ones with a full complement of wheels and mechanicals, and they are of better than BSO quality, then I would say a tenner a pop is probably not far off.
Most of the secondhand bikes I have purchased needed very little spending on them mechanically. I don't routinely replace cables, so long as they are not frayed and in danger of snapping. I just lubricate and adjust the ones that come with the bike. The item I replace most often are tyres, but that's only because I want puncture resistance if the bike is deemed better than a pub hack. Even most of the old tyres that come with my secondhand bikes have plenty of miles left in them, and do not really need changing, if puncture resistance is not the main criteria. I keep and use them for local rides only.