The technical expertise required to do so is very limited as long as you don't password-protect the BIOS: Basically, they only need to be able to plug in a USB stick and reconfigure the BIOS to boot from it.
In other words: If you leave your laptop outside of your physical control for even a few minutes, you may have to assume that it is totally compromised as long as you don't have a BIOS password.
If the laptop is outside of your control for a longer period of time, you probably have to assume that it has passed through the hands of somebody with sufficient technological know-how to work around the BIOS password as well.
For non-soldered but socketed BIOSes I think one can just take chip out and put it into your wallet, possibly, covering some pins with some dissolvable insulating substance. For soldered SPI EEPROM chips with known pinout, I think one can reflash the chip afterwards.
I had a Thinkpad T42 on which I managed to set a password for editing BIOS settings that I did not remember.
I the laptop into IBM for repairs to the monitor, and as part of their repairs they needed to get into the BIOS settings (I believe to run a diagnostic). Their solution was to replace the entire motherboard.
I was 99% positive the same could be achieved by messing with EEPROM. And, indeed, less than 10 minutes of searching yielded this unsurprising result: http://arduino.ada-language.com/recovering-ibm-thinkpad-t42-...
tl;dr: Nope, T42's BIOS password is not secure if you allow anyone with necessary hardware to touch the motherboard for a minute. TPM may (depending on the laptop model and firmware revision) prevent password recovery but will likely not prevent anyone from resetting them - at least this seems to be the case with Thinkpads. Next time I'll clean dust from my X300, maybe I'll remember this thread and check its EEPROM too. :)
So, do not rely on BIOS passwords as a strong security measure.
Craigslist.
Or eBay, or Kijiji, or the Classified section of your local newspaper. Whatever lets you get rid of your possibly contaminated device while recouping at least part of the cost.
The difference between the price of the new device and the amount you can recoup by selling it secondhand, multiplied by the probability that your device will indeed be seized, should be considered an integral part of your budget for any international trip. It's just one of the many ways in which tyrannical governments increase friction in their citizens' daily lives.
Rather than leaving it at home, a trusted third-party service could supply a image/reimaging service at popular travel endpoints.
A lot of risk in it I suppose.
That's a big problem.
edit: To those below: True. I thought about hardware after I posted; didn't even think about the BIOS thing but that's a great point.
Your data should stay at home and a VPN connection to your home PC would be a good first step.
That is unless you believe that those prying authorities have the will and the way to leave an undetectable backdoor in your laptop. Breaking the chain of custody in any laptop today is akin to destruction of trust in that device. Who is responsible then for paying for this damage?