Shaking when I accelerate and check engine

So I was at a stop today and everything was fine. I started accelerating and everything started shaking and the check engine light came on. I went to Autozone to have them run a diagnostic. It came up with the following codes:
P0305 - Misfire on cylinder 5
P0441 - No purge flow detected
P1250 - PRC Solenoid Circuit Malfunction
P1478 - Evap small emission leak
What could be the problem and is it an expensive fix?

2000 323i, Manual Transmission, 105k miles.

I would say the biggest problem to tackle is the misfire on cylinder 5. That, however, could be multiple things- spark plug, coil, or injector. There are DIYs on how to find out which problem it is, just do a search. I cannot give any insight on the other codes... there is a chance that they may have been stored codes as well. Did you have them reset the codes?

Where is the best place to buy coil packs? Which spark plugs would you recommend? and I plan on putting some sea foam through it to clean the injectors unless someone can recommend something better.

Check Pelicanparts, Autohausaz, Bavauto for coil packs. There are also several vendors that endorse this site that you can try looking into. When I replaced my spark plugs, I went with NGK. Once you enter year year and model on Pelicanparts or Autohausaz it will give you only plugs that will fit your car. Check out ebay for used coil packs too, sometimes people are selling stock ones after an upgrade.
I would run some Lucas fuel and injector cleaner through the system as opposed to the Seafoam. I have used Lucas and Chevron Techron before and I like Lucas just a little bit better. This may not solve the issue though- when my 5er starting throwing a misfire code, I ended up pulling the fuel rail and you couldn't even recognize the injectors from underneath all the carbon that was built up in it. I hope it's not too bad for you

Check to see if gas cap is tight
Check for vac leaks on intake tract
Change fuel filter