Don't fret too much over Rh and having a tent. Cheap mylar blankets areexcellent for tacking onto walls to make your own tent... it won't be airtight, but I can't see the need for being airtight except possibly for ventilation purposes. Temps up to 85 are fine and temp control can vary a lot. My temps range rom 63 to about 86 between light/dark, and my humidity is always low... 40% in summer, 10% during the winter... things still grow well. Try to keep your roots from getting too cold and your temps warm. A lot of the "professional" recommendations for temps and humidity isn't always the case, and folks grew just fine before the advent of all of the new gadgets being sold for high prices.
Growing is alot like having your first kid... you double check every drop of water, Ph adjust, test PPMs daily, flip out over a yellowed leaf tip... you can see where I'm going with this. After you have a few grows under your belt, you sort of laugh at how seriously you took each task instead of letting the plants do the growing after you set them up properly from the start. I get bored as hell... if it wasn't for watering, I wouldn't need to see them for weeks on end.
Your $450 investment in lights will serve you well for years, hopefully. Your price will drop once you get things rolling, as the initial startup is the expensive part... later grows are pretty cheap!
