Sannies seeds, cheap, awesome.
PeakseedsBC, cheap, awesome.
The list goes on, but they stand out to me. Peak is especially cheap considering you can buy fairly true breeding seeds from him that would be very suitable for breeding and are very good quality.
Sannie similarly has a lot of great potential breeding material for cheap. You should note that breeding material is the kind of thing a lot of other vendors don't release for many reasons. Easy to replicate true breeding strains, takes more work to stabilize etc. He also has some really outstanding F1 crosses. Check out my Sugar Punch smoke report. It's the kind of thing you can expect.
In the end, you need to do thorough research yourself on everything you're interested in. Check out breeders descriptions and such, but don't swear by them because quite frankly there are a lot of shady cats in the game.
Sannie and Peak both have outstanding customer service and the descriptions are accurate and the pictures legit.
BC Bud Depot for example rips off other peoples pictures and slaps big names on random genetics in an attempt to make bucks dishonestly. You might still get good plants from them, but I'm not sure they're an outfit worth supporting. Not to pick on them (well maybe a little, they also ripped off a strain whose creator demanded be given away to anyone who wanted it for free called Free Leonard), but they're a pretty good example of a middle ground.
Doggies nuts is a good example of someone attempting to blatantly rip you off.
In the end research is always going to be your best option. And take everyones opinions with grains of salt because quite frankly some are a lot more valid than others for all sorts of reasons. Level of education, experience, conflicts of interest, indica lover vs sativa lover etc etc etc etc.