Its not likely you'll find a clamshell style woody for under $600 these days but a monorail or a Speeder for sure! You can take monorails and Speeders afield and most will behave well on a heavy MF sized tripod. Speeders will also permit handheld photography and are also fine for portraits (john nanian, who posts here, does incredibly beautiful portraits with a Speeder) A monorail OTOH will give you all the movements you could ever want and I think would be a great tool for learning.