There are a couple of major differences. One, the Russians don't try to compete with a worldwide navy with carrier battle groups, they have a navy that (Aside from some still-serviceable boomers) is just designed to support operations in and around Russian home waters with the occasional show-the-flag trip. Two, their strategic focus is on stuff they can drive to, plus a little bit of low-cost screwing with us with a few Bears flying out of northern bases, not maintaining and supporting a global presence able to project force anywhere in the world and fully support it. Three, the US will buy a billion dollar airplane so we won't lose an airplane in combat, while the Russians will build a bunch of 2-million dollar airplanes and be perfectly cool with losing a couple of them as long as enough of the rest of them get through, really a lot like their philosophy about Stalin tanks vs. Tigers (Notice that the guys who used the Tigers aren't around anymore). Five, there is the whole political will thing.
A dollar-for-dollar comparison is really not all that meaningful. Look at what the US spent on Viet Nam and what the North spent on it, and then think about how it came out with a lot of those same differentials in play.