As eyeinthesky says, it depends on why you're looking at twins. If you want to regularly haul 4+ people, you may want to think bigger. If you just want the security of a second engine for you and one or sometimes two passengers, a smaller twin will work out much cheaper.
I think it's hard to beat the Twin Comanche. With two 160 hp engines and a MTOW under 2 tons, it's a 150 KTAS cruiser in airways on 13 USG/hr avoiding nav charges. But the aircraft is necessarily old (production ceased more than 30 years ago). Its successors, the Seminole and to an extent the Seneca, don't have all of the advantages.