Greetings Dalma and welcome to the 501st.
Like you, I too have been searching for "vendors" that are willing to either build the armor (fully commission) or have parts that are 501st requirements. When I joined in 2008 the competition on the market weren't really out there until now.
(What I mean by this - there weren't many vendors who were making armors that met the 501st requirements.) I still remembering seeing on eBay for a Stormtrooper armor for $800 + shipping which look really "Halloween" and flimsy and wasn't even made out of ABS or PVC, which is a red a flag. I would advise you stay away from those.
Thankfully times have changed and now the market is more saturated with really good products out there. Of course the higher the quality the more expensive it is, which is also a reminder of how much you can afford or willing to invest.
If you're like me who lives in a small complex unit, and have no access to tools or garage/work bench I would definitely think about getting a commission armor, something basic that doesn't require a lot of details. For example a Stormtrooper - ANH or ESB.
You mention "Propmasters" and I'm not sure which one you're talking about since there are (2) in the UK (That I know off, I could be wrong - if so please correct me.)
-Propmasters.net - is one that I've heard before with also some backlash reviews, I think it's mainly a collectible type and not really "Cosplay" material (I could be wrong) however having some friends who ordered from them, they weren't happy at all so I would advise you stay away from them.
- RS Propmasters - is one that has been recently new and it getting well earn reputation for the accuracy and attention to details. Why? This is one company who had access to the original molds and details which means more appealing to the public and those SW Events. You can get a fully commission suit from this company that also gives you step-by-step easy installation using Velcro.
Personal opinion: I plan on purchasing my stormtrooper from this company soon. Con: It's going to be expensive no doubt but a worthy investment.
You can also get the un-build version as well, which is cheaper but you'll have to find other vendors for the neck seal, under suit, blasters etc. Of course, you'll have to build it yourself which can give you more freedom in fitting.
- 850 Armor Works - this is one site, that I've purchase my shoretrooper squad leader kits from, the price is fair, and the quality is good. The only con I have with this company that it takes AGES. This is due to high demand of various armors being made. Since they don't make them in singles, pretty much your armor is combine with other armors that are similar. I'm still awaiting parts and its been a year...
I know this is a long response, but I hope this has given you some insight as well and for anyone else who is new.
Keynotes:
- Make sure your armor is ABS or PVC and meets 501st CRL Requirements.
- Don't buy from eBay
- Decent armor can cost around a few hundred dollars to thousands. Anything below $50 is not ideal, unless your a lucky person who bid the armor on ebay for 50.
- look on Esty (but be careful) again pay attention to details what looks movie accurate vs Halloween can give you a second perspective.