Do I need to pay VAT or import taxes for shipping my PC setup to Thailand for my workation?

If you're putting all the components in a carry-on, just check the weight limit of carry-on baggage for your airline, or purchase excess carry-on from the airline before hand. Most airlines generally have 7kgs hard limit on the carry-on baggage weight.

I don't quite remember the exact amount because it was couple years ago. I purchased a cheap case for about 2K Baht. I think I only paid about 800 baht extra for them to assemble it for me and do a 10 minute stress test to check every component is working fine. They might have increased the rates now, but I'm not sure. However, any PC shop here will offer you PC assembling service as that's one of their core services. Just shop around for rates. Every mall in Thailand has at least a couple PC shops. JIB, Powerbuy and Banana IT are widespread. There are also many small individual players in malls such as MBK in Bangkok where you might find better rates for more personalized service.

Don't believe the customs of Thailand. Even if the item is clearly old, they'll charge you as if you're importing a brand new item. The price you declare in the shipping form is useless and you'll have no recourse to counter the amount they charged you as VAT, which can be as high as 33% of the "value" of the item you're importing. Here the "value" is what they find online for a same new item and will charge you VAT accordingly. Different PC components can cost different amount of VAT depending upon what category that item falls under. So essentially at the end, Shipping + VAT will cost you almost the same as a new PC build.

@Kevin *******

I packed my PC as is with some bubble wrap inside and out within my bag then told the desk agent that it is a computer so please take care. Never have any problems, not even a single dent.