ANOVOS has two lines within their TOS 3rd season products. Their premier line is replica accurate in terms of the double knit material, construction, and colors but you may need a bank loan to buy one as they start at $300. Their standard line uses different materials and generic colors which they call "idealized" colors and marketed more to the cosplay crowd rather than TOS replica collectors. To be honest, I would not buy any of the STANDARD line as there are better alternatives at lower prices amongst the independent TOS costume makers.
The ANOVOS has cachet since its an officially licensed product and can probably be resold as a collectible. But that's a lot of coin for a costume you may want to wear and get all schwetty and wear and tear to a Con, or Halloween party.
You can buy a custom made Joseph Kerezman for cheaper on eBay (Joannes_friends) than an ANOVOS if you want that 3rd season double knit nylon although he also offers velour versions as well. He's a former professional film and TV costume designer with IMDB credits and uses that expertise to source out screen accurate fabrics and is known for his high quality TOS braids and insignias. He got a bad rep a few years ago on some ST TOS boards because he didn't fill out or deliver all his orders but he did eventually refund everyone and apparently his service has improved. The only criticism I have about the Kerezman is that the fabric edges on the inside are not finished with a surge, or zig zag locking stitch which would prevent fraying from wear and tear. However, there's no denying that it's very hard to distinguish the difference between his 3rd season Kirk tunic, with the much higher priced ANOVOS Premier, and the Kerezman is certainly more replica accurate than the ANOVOS Standard line.
As others have mentioned Murraymousie on eBay makes high quality made-to-order TOS uniforms at the lowest prices ($99) and possibly the highest service. The fit and finish are excellent. Her outfits look like how the 1st season uniforms appears on TV rather than the ANOVOS Premier and Kerezman approach of how they looked like in real life (eg green colored double knit instead of gold). I suppose you can refer to the ANOVOS as REAL accurate and murraymousie's as REEL (canon) accurate depending on your objectives. For example, you may not want the REAL avocado green colored 3rd season command uniform since people will keep asking why it's not gold and then you having to explain how the 3rd season tunics were green but appeared gold under studio lights theory.
Murraymousie selects off-the-rack cotton velour colors that look like how they appear in the 1st season episodes on TV. For example, the command gold is a "dirty gold" with chartreuse undertones in bright light which morphs into that honey gold color under indirect light just like on TV. You can specify custom features like different fabric as well (e.g. the "Kirk Gold" type craft velour fabric) although it may cost a bit more for her to source it out and take a bit longer to get the costume completed. Personally I would ask for the optional 22 inch hidden zipper option (free) and have her leave off the braids as the ones she uses are imagineered and not accurate. Or else ask how much screen accurate braids would be.
There is also Xscapes who also push for accuracy, and the new kid on the block, Bad Wolf Costumes whose stuff looks good on their website. They sell for around $200.
Finally, the last option is to make it yourself by buying the official pattern and sourcing out fabrics. Personally I'd sooner even modify a plain yellow, red, or blue long sleeve t-shirt rather than some of those awful cheap repros that come along to your local K-Mart esp during Halloween time.
Do those guys modelling the TOS tops at Rubies website look less than enthusiastic? They all look like they're hoping no one from their former high school sees them before their first class reunion.