When I am willing to take in a mixed breed (which is most the time LOL), I usually go to a rescue/shelter/pound. We got Mario for 78.00. That included his neutering, rabies shot and a heart worm test. The place we got him from actually under wrote part of his medical bill. Way too many dogs are euthanized in shelters partly due to puppy mills and BYB. IMO, the best solution is to not support those and instead to adopt the ones already in shelters.
In a few weeks I will have a better idea what breed Mario is. We did a DNA test on him just for fun. He is an awesome, smart dog with an ideal personality. Hopefully he will be as healthy as he is happy

.
Good luck in your search.