I'll dump some info since I used to commission paint.
I'd recommend hunting through local groups, local painters, or some local kid you know has painted other armies to get tabletop quality for a good price. Cash is king since venmo and paypal get 1099's. A good deal would be under $1000 for an army since an average 2k
40k army might be 50-80 hours to build and paint. This also avoids getting scammed since you know the person and can small claims them. Get a contract if they do want to pay taxes on it to lock you in. Vibe the painter out and get recommendations
A local kid trying to get experience might do it for less than 1k for the build paint. I used to do armies for 300 build 600-900 to paint back in 2011-2015 but with inflation anything under 1k is a great pitch price. The majority of commission painters I talk $$$ with make $15/
hr but its work from home so not too terrible. This is for lower end table top quality or 12/20 paint scores at
GTs. Most clients are also repeat customers. I have about 5 clients that all paid me 10k ea~ over 5 years from various add on to their armies. Turn around time for a 100 model army should be 8 weeks or so. I used to x2 the price if it was a tournament rush paint. I havent taken commissions for about 2 years since its not worth my time. A lot of professional painters hit a weird point where their reguarl job is paying x2 or x3 their painting hours. This is why the majority of good commissions painters are over in the
EU (My friend commission painter over in the Ukraine lives "well" off 2kusd/month and just paints an army a month over there full time but he's young)
If if a painter is taking more than 3 months and he's not charging you a severely discounted rate - something is up. You need
WIP photos weekly to be a professional with lightboxes. When I paint an army without a deadline for a friend (I did some super low quality imperial fists awhile back but I had a year to paint them) the price was 60% off since I've painted for the client for ten years.
If you cant paint due to disability - Mitch talks about painting with Parkinsons and he tends to hire lads to assist in some projects. Great guy and talks about the subject.
https://www.youtube.com/user/Terrainosaur
On the two ends of the spectrum from high to low quality :
Siege Studios are great. Army projects tend to be 2-3k usd starting ~ but you should max out paint scores at most events. GMM studios is super booked out but also top notch quality and priced around the same.
Blue table painting on the other hand is [redacted] for more then a decade and legions of clients can back this up. Avoid avoid.
Good luck! do some research! Instagram is probably the best tool to use after Zuckerbook.