(kat's husband and resident Transformer expert reporting)

I'm afraid eBay is your best bet.  It's where I got mine and the only place you'll likely find one these days outside of local ads. 

Moreover, you may or may not be aware, but Starscream is one of the worst Transformers as far as his detachable pieces are concerned.  You basically take him apart for the majority of his transformation and reassemble him after the modifications to his fuselage have been made.  Because of this, most of his listings will be incomplete.  It probably took me 5+ separate auctions before I acquired all the pieces (wings, landing gear, missile launchers) necessary to assemble a near complete Starscream.  And that doesn't even include the stickers, which will likely need to be reproductions of the originals.  So if you can find a 100% complete one at a price you're comfortable with, you'll probably want to go with that.

Sorry I couldn't be more help.

I did find one seller that's always treated me well and does have a couple of listings for Starscream in complete and piecemeal form.  I will PM you the link to his store, but it goes by the name of Wheeljackslab.

added Dazzlekitty, wystearya, beachball, and tempertie.

My FC is 0533-4660-3797  Electric friend safari.

FC 0533-4660-3797  Friend safari type - elec.  So....just lemme know if you add me and I'll add you.  Already added Rosencrantz, melipuffles , Milky, Aitsuki, ponygirl74, Uninu, Tagi, and Dainty.

Oh, and I'm kaos_kat's husband, so I promise to be good on penalty of whatever she does to me as punishment. 

I can provide prices for most/all of those transformers listed, but the method I use (averaging prices of items sold on ebay and other sites) is something that you can do on your own, if you would rather be certain of the numbers provided.

Razorclaw (the lion) - Seems people expect to get about $30 for him, but I don't see anything with bids, even the auctions with notably lower prices or that include other figures along with him.  Should be considered low demand, even if the price is valid.

Prowl (police car) - Fairly common, but he is a first year release.  Loose, without accessories and in good condition (which yours appears to be) expect $30-50, possibly more.

Windcharger (red car) - $10-15 with a little wiggle room on either side depending on condition.  An extremely common first year "mini car."

Freeway (blue car) - a cheap late release Transformer with a simple transformation gimick common to all Throttlebots.  I saw him priced as low as $4 and as high as $20, but expect a low price to prevail.  This line is not generally sought after.

Scamper (black car) - kind of cool for the fact that he is a tiny little guy included with Metroplex, the giant transformer that becomes a city and mobile command center.  As yours appears to have his guns/arms, I'd expect about $20 more or less (found him priced as high as $40).  His price drops dramatically without these accessories.

Groove (motorcycle) - a combiner limb belonging to the Defensor.  Without weapons, no more than $10.

All of these prices should be considered a rough estimate.  I am an enthusiast, not an expert.  Hope this helps.

The rubbery ones are known as decoys and came packaged with many standard G1 figures (for target practice, et cetera).  The cat/panther one is Ravage and the purple one on the far right (next to red) is Devastator.  The other purple one appears to be Mirage and the red one looks like Optimus Prime.  Jetfire is in unusually good shape from what I can see.  Are both arms and legs attached?

Used to collect the old MOTU stuff and I'll even pick up the odd piece here and there (mostly to rebuild my childhood collection) but I no longer actively display or seek out anything.

They've covered most of mine by now, what with the robot and various were-beasts, but we're still lacking something with multiple appendages - a spider!  I'd love to see that.  And now that they've released the Siren (mermaid) CAM pack, I'd like to see more done with the lower torso add-on.  Nagas, Centaurs, Fauns, et cetera.  Unlikely, I know, but I can dream.