The lithium metatungstate is quite expensive for this purpose I should find a more affordable chemical equivalent to lithium metatungstate . Thank you in advance for your help.
I recommend sodium polytungstate (SPT, sodium metatungstate) which is cheaper. If you do not need such a high density you can use ammonium metatungstate (AMT) which is even cheaper. Both is directly available at TC-Tungsten Compounds GmbH, Germany (manufacturer price).