What lake are you fishing, funbun ?? If it's a reasonably large lake, there's likely some good contour maps available for it at your local tackle stores or Wally World. If it's a small lake ... there still may be one for it. Just Google the name of the lake and add the words "contour map" ... and that will tell you if any are available.
Entry level depthfinders are fine, and they will find the brushpiles for you ... you'll just have to get close to them, in order for the DF to "see" them. (as per my explanation about cone angles)
I've used "entry level" DF's since the 1970's ... and I've got 3 or 4 dead ones in my closet to prove it Rofl But, I also have an old flasher unit that still works (& is on a friends boat) as well as two regular b/w depthfinders on my current boat. I'm in the process of upgrading the bow unit to a Lowrance Elite 5DSI Depthfinder/Chartplotter. (just a fancy name for a color DF & GPS mapping system)
Before there were any such things as depthfinders, the "old school" way of finding a brushpile was dragging your jigs or minner rigs just off the bottom, as you drifted or paddled your way around Doh Rofl ... and you were guaranteed to find one !! And the more lines you had out, or the more expensive the baits you were using ... the greater the % of the guarantee Hands Clapping
... cp