それだけのかせぎがあるってことはね。
I found this sentence in a book and I can't understand what it means. I did some research and found that それだけの○○がある is a common pattern, but I have no idea what its actual meaning is. I think かせぎ means income or earnings, but I don't know what the rest of the sentence does to that word, can someone explain it to me? Thanks. Edit: Added pic for more context! 
それだけ means either "that much" or "the amount corresponding to that". Here, だけ means "the extent", not "only". For example:
家を建てるにはそれだけのお金が必要です。
- You need that much money to build a house.
(when there's a specific amount of money that has been mentioned)- You need a considerable amount of money (corresponding to the cost) to build a house.
(general statement about the significant cost)
In your case, それだけの稼ぎ means "the income corresponding to that (patterned glass)".
おおよ。そりゃあ、一人前だ。それだけの稼ぎがあるってことはね。
Oh yes. Indeed, (you're) a full-fledged adult. Having enough income to afford it means (that).
