The issue isn't that the can't afford him. They can. They absolutely can. There's no universe in which they can't. Under no cir stances should the team want to stash their first-rounder. It should literally be the guy they hope is the best player. No other contract on the team is worth getting in the way of it. As I said below, if it's the right player and that player can't come over, that's one thing. Even then, as Objective said, it's dicey and should be Plan Z.
The draft isn't ty. That's just the perception of it. Every draft has good players coming out. Even that "horrible" 2013 draft had two HOFers, another All-Star, a borderline All-Star and multiple other max players or solid rotation players. And that's the hindsight worst draft, not the worst draft in terms of expectations. The Spurs need to find the good players in the draft, not just punt because they think it's a crap shoot. We as fans can think that. It's their jobs to make it work.
As far as the money goes, the tax line is projected at $132 Million. They'd easily have enough space to fit everyone in. As you said, the Spurs are a non-playoff team, so why do they care that they have some more holes? If they are really that bad, they should be looking to move guys for parts, which will fill up the roster spots without adding much salary. Moreover, that range is enough to where they don't need to let both Lyles and Poeltl go to get under the tax (they don't actually need to let either go if they don't want to use the MLE).
It's bonkers, man. Of course Lyles is expendable if the alternative is stashing a lottery pick. To say otherwise just doesn't make sense. I don't hate him, but he's just a guy. Hopefully the Spurs draft a PF at 11 and just start him anyway. Push comes to shove, I'd rather keep Lyles and move on from DeRozan, but letting him go along with letting Forbes and Beli walk isn't the worst thing in the world.