I have a custom modification that needs to be done. Is there a site or place to go to where I can put the spec out there and get quotes? I have a quote from NetSuite Professional Services but I am curious about whether they are the best to use or if I can do better with a 3rd party.
There is no common marketplace. You will have to Google and find other partners and ask them for quotes.
Keep in mind vast quality differences between organizations and freelance individuals. You should base your price point on complexity of work, consequences of script failure and need for ongoing relationship/other work. For example, if you need a small script that sends an email when you press a button and it doesn’t really matter if that button ends up not working, go for an inexpensive offshore individual. If you are looking for a huge business-critical script, and you intend to need many more customizations, aim for a better Partner with a good reputation.