For modern budget 34" ultrawides the main options are:
Acer Nitro XV340CK
AOC CU34G2X
ASUS TUF Gaming VG34VQL1B
GIGABYTE G34WQC
MSI Optix MAG342CQR
Samsung G5 LC34G55TWWNXZA
The Acer is a flat IPS panel, all the others are curved VA panels.
I ruled out anything below 1440p (1080p is just garbage, and the budget rules out anything higher than 1440p) and anything below 120Hz (these are all 144-170Hz). There are may other models that would fit your criteria, but most of them are permutations or older models of these.
I haven't used any of these except the AOC, which isn't bad, but it's missing some controls I find critical and doesn't have particularly good overdrive presets.
Were I to try another one of these, I'd probably give the ASUS a shot first.
You can obviously spend a lot more, but in this size and form factor I think it's waste of money to do so.