I'm not sure what inexpensive is for you, but the easiest and cheapest way to get much better sound without breaking the bank is a two step process.
1. Get a new windshield. The cheapest quality option out there IMO is the LongRideShield. longrideshields.com/collections/2015
I'm currently running the Thresher as the weather has started to cool off and it keeps a little more wind from getting into the cockpit area. All summer I ran the Stingray because it let a little more air into the cockpit area. (yes I have both of them, I got them when they first came out and got them for less than 80 bucks a piece. They are a bit more expensive now but still a really good deal. Follow the directions for ordering the right height and you should be fine or call them up they are really nice people to deal with) If you wait a week or two you may be able to get them for a little better price with Columbus day coming up.
2. There are a number of good quality amps to be had for pretty cheap money that work really well in the Shark. Cerwin Vega has the B52 and the B54. Soundstream has the Picasso Nano series. There are a few others that are good quality that wont break the bank but do yourself a favor and stay away from the Boom! stuff. Its way overpriced IMO and not worth it.
The best bang for the buck IMO speaker wise is the Infinity Kappa 6211i. Its a 6.5" coaxial that sounds good, is a ~2ohm speaker and can usually be had on Amazon for a touch over a hundred bucks. Can you buy cheaper or more expensive speakers? YUP but dollar for dollar the Kappas are a great investment when on a budget.
The only other things you will need are a Biketronics BT355 line leveler BT355 HD Radio Line Leveler And Pre-Amp Adapter for 2014 and Up - Biketronics Inc
and an amp install kit. I went to a local stereo shop and got the wire and fuseholder from them and spent less than 30 bucks.
Dont get it professionally installed, you can do this yourself and save money, plus you will get familiar with the Shark. If you take your time it will take you 1/2 a day. If you have had the fairing off and are familiar with the girl a little bit , it can be done in 4 hours or less.
There are a bunch of threads here on the amps and speakers and how to do the install. It really is a straight forward upgrade and you will be happy with the end result. Hopefully you dont end up like some people and get the stereo bug. (i say that like I'm immune from said bug as I toy with the idea of spending more money on new stuff for my stereo)
With a little shopping around this can be done for about 500 bucks, and will sound leaps and bounds better than what you have now.
Hope this helps,