Yes, that's a bit on the slim side for anything decent even in USB DSOs.
Don't forget that bargain basement scopes often don't come with probes and a pair of x1/x10 switchable probes will set you back $50 AUD or more retail. However it wouldn't be a bad idea to go back and edit the thread title to 'Very cheap DSO for electronics beginner and edit the first post to mention you have a limited budget.
Don't rule out CROs, you can get a long way with a decent one, though they are no good for capturing essentially random one-off events, and manual protocol decoding of more than a couple of bytes of serial data is a stone cold bitch of a job to do and highly susceptible to human error, even if you can get the device you are testing to repeat the data in a fast enough loop, + output a pulse once per loop for your delay timebase CRO to trigger on.
Back in the day, I'd decode serial data manually on a CRO, marking the bits on an acetate taped to the screen, for about two bytes worth, with the Y attenuator set to give me about a 1 div high trace of the data with the clock below it then shifting the delay and both channels Y position for the next two bytes etc. till I either had the whole data packet or ran out of space on the acetate. You couldn't pay me to do that nowadays - my eyes aren't getting any younger and if your business is too cheap to buy basic modern testgear, its probably too cheap to reliably make payroll or pay insurance.
If you *ever* find the need to inspect serial data on a CRO, other than checking one repeating byte for levels, risetime and other signal quality issues, its time to get a cheap logic analyser or if your wallet's plump enough, a four channel DSO with protocol decoding like the DS1054Z.