Bugs in a basement aren’t the same kind to bother plants. It’s the ones on other plants you gotta worry about.
I never worry about RH, just vent to the basement. Keep the grow smaller and you can avoid things the need for A/C and humidifiers/dehumidifiers. Then again, most basements east of the Mississippi benefit from a dehumidifier.
Fertilizer is cheap…a lot less than buying weed. MaxiGro/MaxiBloom, Dyna Gro, Veg+Bloom, Megacrop all very very inexpensive options.
Don’t sweat the money. It’s the only hobby that pays for itself and then some. How much you spend a year on weed?