I use a momentary switch .......
my setup
...n2o bottle.....ebay $70
.....one n2o noid....$35
-4 n2o line 4 feet... $20
-4 bottle feed line $40
some wire and a switch from radio shack.....$7
and because I dont rig my stuff...... a relay ...$15
...... came in just at under $200...