You could have the most expensive computer you can imagine and you can't mine with it properly. Either you are going to mine a coin that is so small and mined basically by very few people that you will not really make too much money from it. Or you are going to try to mine something proper and they already have machines upon machines that mine it which means there is no way people could actually get into it with computers.
Right now we are talking about difference of 1 mining equipment mining more than 100 computers, there is no computer that could close that difference, even the 30k dollar computers can't mine ethereum and profit right now. Just keep your laptops life longer and close it when you are not using and not tire your computers cpu and ram so that it can live longer before breaking down.
What are you talking about? First of all there is no such thing as a 30K computer. Maybe the most expensive computer these days is $5K or so. And ETH is still mostly mined by GPUs and they are pretty cheap these days.
You can go on Craiglist and buy an RX 470 8GB GPU for around $100 or so. Get about 5 of these, add a hard drive, cpu, ram, big PSU and you got yourself a rig for probably less than $1K. There are ASICs out for ETH but they aren't that much more efficient in terms of profitability.
BTC is a different story. You can't GPU or CPU mine BTC anymore. ASICs are the only way to go for BTC.