Well.....for me I'm on the low budget end of the hobby for now anyway. I like to tinker and don't mind building them, I've done a Tonka dump truck and am in the later stages of a Bruder Delta loader. I have several Bruder, Tonka and Nylint construction toys I want to convert.
RC4WD sells some nice construction equipment, as does MAGOM
https://store.rc4wd.com/
https://www.magomhrc.com/en/
A little less expensive and will probably require some tinkering is Huina some of their stuff looks pretty nice and it seems most people are happy with what they get.
This guy seems to get good revies for sales and service
https://www.xtreemrc.com/
and there is always Banggood...but prepare to wait, they take forever to ship
For conversion I use WPL/JJRC bits and pieces....not top of the line but they are reasonably priced and have worked well for me so far....
So you see there is a wide range of trucks it just depends on how much you want to work on them and how much you want to spend...Hope that helps a little.
I'm sure others will be along with more information.