Max, raising prices isn't ripping off. The term implies he's dishonest.

I don't know this guy and have zero interest in the kit, but it's his and he's allowed to price however he wants. You just missed a great price. At roughly $15 a pound for silicone and a kit that size will eat up at least 20 lbs by a good mold maker, you do the math. Good resin is $90 a gallon. Not having the kit in front of me to measure, I'd guess he'd be getting less than 10 per gallon. And a bubble can ruin your day. A bubble in $300 worth of silicone can ruin your week.

There can be a thousand reasons to raise prices from initial offering. Maybe he had 10 sets @ $120 and blew through them. Heck, when I was making those tools, every production run got more expensive, the most laughable was a part we paid $1.25 for the first 100 pieces went to over $8 a month later. Same place, same material, just a ridiculous change. What happened in a month? The laser didn't get more expensive, I doubt the operator's salary increased 6 times, we gave them the steel sheet, dropped off and picked up. You think the end user could give a rat's arse about that when the price went up?

You can say he's too expensive, you can say you won't buy it, but not that he's dishonest.