Yes, semi-hydro (SH) is a way of growing, but not a way of curing a dying or half-dead orchid. If they've been growing in a bark mix, etc, and killing them, then you switch them to SH with no new active root growth, you're setting yourself up to lose them. Whatever roots they have will not survive the transfer, and without new roots just commencing it will likely be their death warrant.
If you want to change the way you grow from one medium to another (bark to SH for example) then get them healthy enough first to stimulate root growth. SH is not a cure-all, it's only a different cultural method.
Welcome to OB. Ask some more questions first. For cheap effective starting pots, get some pint or quart deli containers, or tupperware type containers. Anything easily drilled. Can even start with a 2 liter soda bottle with top cut off.
Perhaps post some pictures of the orchids you're trying to save so we can help you a bit more.
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Caveat: Everything suggested is based on my environment and culture. Please adjust accordingly.
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