Irgacur can be easily dissolved in DMSO at the concentration of 0,5 % w/v.
PEDdA can be dissolved in water. Pay attention to the concentration of PEGdA in solution. The mechanical strength of the hydrogel depends on the cross-linking density so, if you want to obtain soft hydogel, I recommend to not to exceed the concentration of 15% w/v of PEGdA in water. Ethanol is not recommended as it acts as a radical scavanger some times. Methanol is toxic for cells, so DMSO shall be the best choice if you are looking to prepare hydrogels for cell culture.
I would like to suggest not to use Irgacure due to its low solubility in water. better instead use LAP (0.25% wrt PEGDA). It has good water solubility as well in PBS.