Any oscilloscope is better than no oscilloscope. (But the virtual oscilloscopes -the soundcard ones - are toys at best, I'm not considering them in this discussion).
You can buy a used oscilloscope for less than $100 so if you're serious about electronics repairing then you definitely need an oscilloscope. Just buy whatever you can afford, even if it is just a 10MHz scope, it is better than nothing. When you have more money, buy a more expensive one. I have two, and I use both.