can't compare a cello to a bass for ya, but to suggest you start on guitar instead of bass if you want to play bass is the same as suggesting you take a trip to Mars when you really want to go to the moon -- make NO sense at all. What kind of teacher do you have?
As for a "cheap" bass amp, if you want BIG and cheap, look for used Peavey Combo's on Craigslist. usually get them under $200 no problem. If you want a small, cheap and good practice amp, look for a Peavey Microbass. Of all the teeny tiny bass amps I have tried, this is by far the best for the money and the sound you will get out of it. This is not to say I am some sort of Peavey fan, but those would be your best choices.