yes, all in all the 350 is usually cheaper power. dollar for dollar the 350 will make more power, that being said, it doesnt mean a 305 cant perform.
they share the same stroke...if you use it as just a driver, not making the engine work hard, the 305 MAY get slightly better MPG.
by comparison, if the 305 has to struggle to pull a heavy load, while the 350 doesnt, the 350 will likely get better MPG.
as far as rebuilding cost. 350 is cheaper. a stock rebuild kit for a 350 is 158.00, while the same kit for the 305 is around 250-300. more people rebuild 350s....so mass production decreases costs.
Ive built a couple 305s..just to try it, & they both performed great, one ran 13.70s in my 3.08 geared GMC Caballero & pulled 14" of vacum..so obviously nothing radical.