I disagree with those figures complete, Solanke will be on double that at least. He walked out on Chelsea who offered him a new deal (they've just offered Hudson Smith £85k per week to stay who is regarded very highly as Solanke was at that time) as Liverpool offered him more and then he's just left them and signed for Bournmouth for £19 million so no way did he take a reduction.
However even if we use your figure of £30,000 per week, Sandro cost half what Solanke does:
Solanke: £30k per week for 3 years + a £19 million transfer fee = £23,680,000.
Sandro: £80k per week for 3 years + 0 transfer fee = £12,480,00
Sandro has actually done something in his career and once scored 20 league goals in one of the top 2 leagues in world football.
Solanke has done absolutely nothing, ever.