Hi thought this may be of some use
Visionking optics are doing 2x, 3x, 5x 4 element barlow's for £45 on e-bay
I asked if they are telecentric and the cap I spoke to was not sure so he stiped one down and sent photos for me
Definitely looks correct
so if you are building a solar scope or just need a better barlow useful for solar work they are certainly a lot cheaper than a power mate and look very well made.
Hope this is some use to someone.
I shal be getting one when we get some working filters and decided the best mag to get then I will post the quality of them.