Good decision , rather save more and buy nice unit . Once you have it, it will give you such an advantage - trust me on it .
To give you an example - we went for bass with boat that had side scan. We would never catch so may bass if we did not have it . One instance , we picked what it looked small broken branch close to shore while crawling with electric motor and on side scan showed that is fairly big branch under the water and picked fish ( you could see clearly that was a fish in decent size) hanging just under thicker branch. Reversed a bit and start casting - I was glued to screen from amusement while other guy was casting . I saw fish disappeared from screen - I lift up my head and fish was on the hook. Bass 1.6 kg. Checked after, no more fish there - was only that one , we pushed off.
If we did not have that fish finder we would never catch that fish and if we did we will be casting for at least 1/2 hour after, thinking there must be more of them.