In my dirted tanks, it usually takes about 6 weeks before the water chemistry settles down. That seems to be about how long it takes a tank to cycle anyway, so to me it's just cycling the natural way. As soon as Amonia and Nitrite are at 0 and the plants are growing robustly, I know it's time to add fish.
For affordable plants: In Washington state, check out TheWetSpot. They have a great selection of plants and shipping shouldn't be too much. I've also had great luck with Buceplant.com. Amazon, Ebay, and Etsy are worth a look, too, though they're a risk. Make sure you only buy from sellers with really good rep, and make sure they're in North America. I have mistakenly ordered from East Asia or Europe a few times, and they tend to not thrive on the journey. Ebay and etsy plants tend to be infested with snails and other interesting inverts. I like inverts so this isn't a problem for me; anything parasitic or pathogenic will be long gone by the time six weeks has gone by. But some people hate snails and worms and such, so if that's you, be aware.