When considering a 335 vs 340, all costs with the exception of maintaining the pressurization system, insurance and recurrent training are about equal between the two models. I currently own a 340A and have to say the pressurization maintenance is minimal. The benefits of pressurization far outweigh the expenses in my opinion. I would venture to say that I have not spent more than $1,200 over the last 5-6 years on the pressure system. We could debate the need for recurrent training all day; I am of the school that every pilot should be required to attend annual training if you plan to fly actual IMC and require predictable utility from your aircraft. I use Recurrent Training Center in Champaign IL. The training costs are about $1,500 and it is worth every penny! I learn something new every year without fail. You may want to join The Twin Cessna Flyer
www.twincessna.org, Larry Ball would be happy to give you the facts when it come to real world comps between twin cessna models. Hope this helps.