Mono Montana is a good starting deck, especially if you've got Hugo. Except for Mona, most of the cards are under 2K and you can build a pretty good deck. You need Spiaghi and Oscar, and Edd is probably your best 4* option, but the rest of the cards depend on your taste.
Mono Rescue is another good choice. Splurge on a good 5* (Aurora or Hax; Sledg seems to be banned every other week). Of the remaining cards, only Anita and Elvira cost over 1K if you're willing to do without Kerry.
Another common cheap deck is half Roots, with Jeto, Rico, Yookie and Noodile combining for 11* and a little over 1K clintz all told. This leaves you most of your budget to pick the other half; go nuts!
There are plenty of other possibilities. These are just some of the more common ones to get you started.
Rescue and Hugo + Montana are the obvious picks... what is great about them is you can do well in DTs and get decent ELO scores with them too
for an alternative... use Roots. the half deck of Jeto Rico Noodile and Yookie is dirt cheap... maybe 1800 clintz or even less
and then pair it up with say another good half deck with Bangers like Chlora Graff Bball Loocio maybe even Bodenpower. that half deck would only cost you 3000-4000
so for less than 6000 clintz you have a deck that should easily make 1300 in ELO
Here are a few examples of decks within your budget to give you some ideas:
Montana - deleted - 5k (can switch Donnie to Edd within your budget or change Don to Hugo)
Ulu Watu - deleted - 9k
Roots - deleted - 7k
Roots/GHEIST - Anti Cooper, Anti tectonica - 8k
Piranas/Bangers - deleted - 10k