There are a ton of variables in regard to cost as your post is stated—it is far too vague. To estimate cost one would need to know at least what you are painting. Even if one assumes you have a VTX 1800 you want to re-paint, it would help to know if the base color of the tins is already black. The VTX engines can be blacked out with a lot of labor and relatively cheap cost. Here is a link to see just what's involved in doing the engine: https://www.vtxoa.com/forums/7-vtx-1...ell-i-did.html
In any event, I'll toss out what I know about the custom painting I've done.
If you are totally inexperienced with painting, you probably are vastly underestimating how many hours it takes to do it right. Much of the labor involved is prepping the surface to be painted. Simply painting a stock silver colored side cover to a satin black would involve sanding the surface smooth & flat, painting at least a coat of primer, (allow to dry) a coat of satin black, (allow to dry) wet sand, and then at least another coat of black (allow to dry and repeat wet sand and repaint if any defects are found) and I'm making it simpler than it would likely require for a show room look. The paint and materials cost are not typically what keeps people from custom painting their rides, it's all the hours of prep and labor involved in multiple coats of paint that are the real deciding factor.
A vinyl seat can be repainted with very good results (I've done one) such that if you wanted a black seat painted red it could be done cheaply (takes about 3 coats to do it right) with a quality vinyl paint. Spray painting chrome parts can be done, but it involves a lot of sanding. I spray painted my plasti-chrome engine covers on my VStar 1100 with high temp paint and it has held up nicely, but was a lot of labor sanding the chrome down evenly. Chrome is a tough metal so it's a LOT of work. You'll need a metal etching primer coat 1st, then wet sand, then another coat of paint, wet sand, repeat.
Some guys have had good luck painting over chrome (blacking out a bike) that isn't high temp engine parts with a rubber based paint called Plasti Dip
. I've painted a few chrome parts and had good luck with the durability. The paint comes in various colors too. The easiest way to get the blacked out exhaust look is to buy black pipes, otherwise you are again dealing with the labor of sanding the chrome to paint it, or pay to have it sand blasted and ceramic coated.
If you're serious about getting into DIY painting check out some of the many How to paint YouTube videos available to see what's involved.