Online mixing and mastering

Honestly I'd be surprised if even the really big guys in metal were charging close to $30k for an album mix in this climate. I know of one very well renowned metal-mixing Swede who recently mixed & mastered a local band's album for about 1/3rd of that.

Times are tough! Those figures are probably only reserved for the guys working at the top of more mainstream genres.

That said, $100 is very conservative, and as Jenk said above here in Oz that wouldn't get you a 'professional' engineer. I would suggest perhaps looking for engineers in places such as Poland, where the budgets are more in line with the country's economic climate.