Getting visas for Afghanistan is becoming easier. Visas are being issued at most consulates and embassies, and cost around US$50 for 30 days for a tourist visa to US$160 for a work visa and US passport holders. Visas can easily be extended.
You may need a letter of introduction and sponsership. Rules and rates for differ depending on the embassy you use.
Afghanistan Visa information
Afghanistan Embassies
More Afghanistan Visa information