1. nashbar carbon disc fork is $120-150 (depending on sale). ebay is another good option for very light fork...but buy from a seller with excellent reviews.
2. light ~300 gm folders: https://www.biketiresdirect.com/prod...d-prix-26-inch
3. you may be able to find wheels that weigh less than 1700 gm for under $500
Here is one example:
Easton XC One Disc Wheelset - 6 Bolt Int Standard | TotalCycling.com

Another option may be to convert your bike to 29 inch...many mtbs can take road disc wheels with little impact on handling. This would open a whole range of road disc wheel options and would allow for narrower high-pressure tires.