UKC

I want a power meter, but there don't seem to be any that fit my cranks (fsa omega)

 so perhaps I change my cranks, but that also requires changing the BB, and everything seems to be 111/12 speed nowadays... But I'm on a ten speed system. I'd rather not have to change my entire drive chain to get a power meter fitted, so I may as well buy a new bike, right?

Alternatively I could find a new crank set up that fits my current chain rings, and swap it out, more research to do in that I think.

Or get pedal based power meters, but they look like they cost more than my bike did... And don't even fit my spds...

After all this I'm not sure I can be bothered with it and will just stick to HR based training metrics.

Anyone else had similar trouble getting set up? I have these thoughts every year or so and never get anywhere 

GTE

I had an 11 speed SRAM Force power2max crank that I used on both Shimano and SRAM 10 speed. No issues using 11 speed chainrings, I still do now. I used to swap the whole crank between bikes when I needed to, took a couple of minutes with a SRAM crank. That PM died after about 10 years of use (metal around locking boly failed) and I swapped over to Garmin Vector 3's, which I got refurbished from ProBikeKit, they appeared to be new but were £400. Have had them for 18 months, had no issues with them. I'd recommend either based on my experience. YMMV

I had exactly the same dilemma, and decided that sticking to the HRM was probably good enough for a (keen) amateur like me.

I figured that when I eventually get around to replacing my road bike I'd probably fork out a little extra for a power metre.

Last time I bought a bike was well before 12-speed existed but 9-10-11 speed were all mutually compatible. 

Edit: If it still exists, it sounds like a question for your local bike shop!

I’ve got rotor crank pm and Assioma pedal pm.  Pedal pm are good because you can transfer between bikes. However unless you are into serious training or TTs I wouldn’t bother and just use the hrm. The power meter will give (almost) instant output levels whereas hr lags. Using both you can get an indication of tiredness etc I do intervals based on pm rather than hr. If you do get a pm it’s worth investing in Joe  Friel’s book .. Power meter handbook

Sounds like power meter pedals would be easier?

Just to complicate it further, the pedals are seized on. Or at least one of them is, despite the best efforts of me, several burly friends, the attention of the local bike shop, and some very long levers... so some crank replacement is likely necessary anyway 

Gte

What crankset do you currently have? You could get a Shimano  105 left crank meter that would work with whatever you like from Shimano on the right. 
 

https://winstanleysbikes.co.uk/stages-g3-power-l-105-r7000-power-meter-cran...

FSA MegaExo cranks are pretty rubbish, so if you're planning on putting a powermeter on the bike, I'd just replace the whole lot with a Shimano crank with PM attached.

For double sided, this realistically is the best option (if you don't mind a 175mm crank):
https://www.cyclepowermeters.com/4iiii/4iiii-105-r7000-precision-pro-instal...
A new bottom bracket is only £20 too:
https://www.merlincycles.com/shimano-ultegra-bbr60-bottom-bracket-62947.htm...

If you're not fussed about double sided you can get up and running for just £430:
https://www.merlincycles.com/shimano-ultegra-bbr60-bottom-bracket-62947.htm...
https://www.merlincycles.com/shimano-105-r7000-chainset-11-speed-117101.htm...
https://www.merlincycles.com/4iiii-precision-30-105-r7000-powermeter-258987...

Garmin, SRM all make SPD compatible power meter pedals, for a price...

Favero have just released the beta version of their SPD power meter pedals in the Italian market. If you don't mind potentially voiding the warranty it is also possible to fit SPD compatible bodies to their road pedal spindles, there is a long running thread on the TrainerRoad forum.

Like you any sort of power meter solution is going to cost me more than my bike is worth. But I would probably rather invest in pedals where the standards have been in place for over 30years rather than a crank based system where BB standards are changing every couple of years, and the cranksets are considered disposable by the manufacturers based on the prohibitive cost of replacement chainrings.

I bough a £499 smart trainer in January 2022 and training with power indoors has made a big difference to my fitness because it takes all the guesswork out of hitting power targets in <1hr sessions. Outdoors I'm still riding to HR and RPE and mostly doing longer endurance rides which can be paced with HR.

TLDR n+1 is the answer

Buy a tube of copaslip anti-seize, and apply to the threads before fitting your new BB and pedals.