the most reliable jet skis on the market is the Yamaha Waverunner series with any doubt!!, you wont get a four stroke yam for that money (even after 3-400 hours they still command 3950 + but you can get a 50 hour xlt 800, Just!! 125 hp twin cyl carbed 2 stroke, very light, use the proper oil and it should last you.(£50 per gallon)
The XLT 1200 3 cyl YAMS are great but really drink the fuel and arent that much quicker, even tho they are 160 hp and some did have middle cylinder issues.
yam waverunners had the water spout but can be re directed
Waverunners have the best hull in terms of comfort followed by the seadoo.
The other yams are the gp series, twin seat and are really are the sporty version of the XLT800 and xlt 1200, except the gp's dont have reverse which can cause general handling issues.
mechanical probs, stay well clear of the early sea doo 4 tecs as nearly all have supercharger issues with sc couplings disintergrating unless they had the titanium upgrade, but still have sensor and other elec probs.
the last one that would fit the bill and i have seen some bargain 4 strokes is the kawasaki STX range, 1200f and 1500f four stroke 4 cyl engine, super smooth, super reliable and you can get a 75 hour plus stx 1200f for 3 k if you keep looking, , reasond mentioned below is that they are not the ski of choice, A friend had the stx 15f, 160hp quiet, economical, hard work and could not stay in easily.there is currently a 15f on flea bay (pictured below), and i dont know the reserve but he would be lucky to get 4250 for it and it looks fantastic.12k new!!
BUT the kwacker hulls are super flat and slam and tram line ALOT, also the foot well is very deep SO if you get flung out, your foot stays in a tad longer than the rest of you, and bloody hurts!!
pics of my old skiis, first one is the xlt 800 2004 model, last one is a fx160 four stroke 2005 and the third one shows the kawasaki that you could get for 3750k area. this one is the 15f but the 12f is achievable for your sort of money
Hope this all helps