again depends how handy you are or what you prefer - but i built my own based on the $3000 usd one here endorsed by Chris Kresser - who usually does his research - and i was more convinced by the near infra red literature than the far infra red stuff
https://sauna.space/productsi used 5 bulbs in place of 4 because i felt the original design lacked coverage of the lower legs
i used an untreated wood frame - and untreated canvas cover
i fitted switches so you could have 2-3-4 or all 5 bulbs light - for adjustability
it worked very well - though not as pretty as the original
total cost around $200usd
photos here - pls excuse the mess i had v little room to work with
https://ibb.co/k48kqskby the way with incandescent bulbs you need not be concerned with EMC issues - they are simply not significant emitters - its more marketing spiel that manufacturers use to try to scare people - i hate that.
i fitted a wire mesh connected to ground over the bulbs in any case - mainly to stop anyone accidentally touching them (they get hot!) - as it took only another 20mins