I have had experience with salinity conversions with both of the fish you have. Both of them can be converted within a few hours, but it is detrimental to the fishes' health to pour large amounts of salt into their water directly. You will have to find a way to remove them from the tank until the salt is mixed and aerated throughly, then convert them and place them into the tank.
Unfortunately, it is highly recommended to purchase at least a little bit of live rock, so you should put away at least $60 for that purpose. The rest can be hand made. If you do not purchase at least a little bit of live rock, the tank will not be colonized by benifitial organisms, greatly reducing your choice of livestock.
Your ammonia spike was caused by a die-off of nitrifying bacteria. If you pour a product such as 'Bio-Spira' into the tank, it will re-colonize the tank and prevent a spike.
-Lynden
