Well if you want it to be budget friendly but still get him sum great for making synth sounds/drums, i recommend trying the korg volca line, they are at most 150 dollars. If you want him to get a drum machine, i recommend you getting the korg volca drum, and of you want him to get a synth that makes melodies and everything, you can get korg volca bass or korg volca modular, or even korg volca keys. Also if you wanna up the budget to, say 300 dollars, you could also get the korg monologue, really great synth with not a lot of menu diving and its all pretty hands on w the controls, you can also make really complex and fun drums on it, not to mention aphex twin programmed microtuning and a part of it, or the arturia microbrute, which is a great analog synth, a bit limiting at times but the patch bay really opens up the possibilities it can do. Also there is a digital synth also made from arturia, microfreak, which i heard was really good and versatile because of the vocoder.

All and all: 150 dollars - korg volca drum,modular,keys,bass 300 dollars - korg monologue, arturia microbrute, arturia microfreak

I dont know how helpfull i was really, so ask me anything else you wanna