Most of what a beginner blames on the instrument is setup, and most of what they blame on themselves is the bow. Neither of those is a spending problem — a modest fiddle that has been properly adjusted plays better than an expensive one nobody has touched, and a well-cared-for bow improves any instrument it is used on.
These guides go in the order the problems actually arrive.
If you are buying
Buy the setup, not the label, and say up front which register you play in — bridge curvature in particular is far easier to specify at the start than to change later. Ask for fine tuners on all four strings, and spend a real share of the budget on the bow.
If you already own one
Check three things before spending anything: that the bridge is standing straight, that the bow has the right amount of rosin, and that the string height is not fighting you. Two of those are free and the third is cheap — and together they fix most instruments that "just feel hard".