Ironically considering the OP and his desire to save money and wave a piece of paper around while declaring peace in our time.
Best way to prepare for a Russian attack is to make sure it never happens
Best way to do that is to support Ukraine, Russia is slogged down in Ukraine, they won't attack Russia. If Ukraine drives Russia out of Ukraine, they won't be all that willing to have a round 2 vs say Poland who is even better prepared than Ukraine to fight back. Also even if Ukraine falls, the show of unity in supporting Ukraine and making it really hurt will send a message that article 5 is a thing, and a message to West Taiwan that trying to reunite with Taiwan is a bad idea.
Supporting Ukraine is a very affordable way to keep Europe, Taiwan and Kpop Korea safe, affordable and actually the best way. It's also a good cause, although I don't care much for that.
It would be another brutal war of attrition if they attacked Sweden. The Russians cannot match Western firepower and will not under Putinesca. Russia's prospects would be even worse against Poland.
A large part of Ukraine's firepower comes from Saab and Bofors.
It wouldn't be another brutal war of attrition. It would be a blitz, well for about a month unless the US gets involved because IIRC Germany and the UK only have enough supplies to go for 2 weeks or a month. Then again maybe that would be enough time to cluster fuck Russia's military. I'd hope Finland, Sweden and Poland are better set up. Those three alone with western equipment and tactics would be enough to fuck Russias shit up.