For the HW95 I'd only consider 177 because 22 would be too slow imo, but your opinion may differ. For ~$100 you can buy a barrel in the other caliber, but you also need the linkage and the pin which is peened in. Or you could make a press fit pin from the shaft of a drill bit I spoze, which people have done with others guns.
Crosman barrels are much cheaper at ~$16, and another $10 or so for all the little parts and linkage. This is one reason I like Crosman so much, parts are available and they're cheap. Plus you can upgrade to a suppressor barrel like the Trail has, so you can buy a cheap referb for $60-80 then get that barrel. Most parts they sell are interchangeable with some other brands, like Stoeger and Gamo. Like Gamo has (imo) ugly stocks, but you can get a nice Crosman stock like the Benjamin Regal for ~$23, and/or that suppressor barrel. Depends on the model as mentioned, but if it fits you could get the other caliber Crosman barrel for your Gamo to see how you like it before buying the HW. Other mfg's are impossible to get parts or they're way too expensive for what you get. The HW barrel is expensive but it's top quality and well worth it so it's actually an excellent deal.
Also know that a Centerpoint you get bundled with a gun will not be as nice as one bought separately. For example the typical 3-9x40AO that's on the Trail is not comparable to the 4-16x40AO commonly available. Mainly clarity, many consider the 3-9 unusable above 6 or 7x. The 4-16 holds up to springers better too. Not just the ones on Crosman/Benj guns are cheezy either, but any low end gun like Ruger or Stoeger etc will likely be the same quality scope, if not the same exact one with a diff name. I still use the cheapie scopes because they do work, but having a Crosman w/ bundled scope and HW w/ nice scope is like having a '90 mustang and a '14 Mercedes, they both do what they're supposed to, but one is clearly better at it and much nicer to use. So many people who buy cheap guns will toss the scope and get a Hawk or Leapers, both of which are very popular for springers.
I also believe the HW is well worth the $. For what you get it's really the better deal. The problem is the 95 isn't as powerful as a generic Crosman, close, and good enough for most people tho., Crosman also makes the XL which HW can't compete with power wise. Take my HW90 for example; 45lbs to cock and 22-23ftlbs power. My XL is 38 to cock and make 28ftlbs. I tuned my XL while the 90 was oem, but the oem XL still wins. The Crosman gains (and any cheap gun) are good because the quality is low and most of the gains are simply fixing the flaws. An HW is high quality but somehow power is lower. I never even opened my HW90 because it was a work or art and I didn't want to scratch it. Anal yes, especially considering I take everything apart for mods so it was killin me, but I just couldn't do it. If/when I get a 95 I will take it apart for tuning, just carefully..
Just a few thoughts on the subject fyi...