Vintage Husqvarna are very popular in Vintage racing. From about 1972-1979 was the peak years for Racing. Although they didn't sell like the Japanese bikes they certainly were competitive. You will see on most score cards a Husqvarna represented well for the above years. They are known for a smooth power-band excellent handling and reliability. They are easy to work on and parts are still available although pricer than older Japanese bikes. An example is a piston ring set for my 1978 250 CR is $170 where as my son's 1979 RM 125 is about $70. Here is a good example of a Newer model RM 250 GP3 following a 1976-78 Husqvarna.
Buying a Husqvarna to race is going to cost a little more than your Japanese Motocrosser. I have recently seen them in craigslist for non-working basket case for $500 to $1500 for clean usable model. A show quality will cost 2500-3000. A professional restored model will cost $ 5000-9000. So you can put in as little or much as you want but Vintage motocross racing is the cheapest form racing you can do.